/* ============================================
   HTML/CSS 학습 가이드 - 통합 스타일시트
   ============================================ */

/* ============================================
   CSS 변수 - 모던 디자인 시스템
   ============================================ */

:root {
  /* ==================== 색상 팔레트 ==================== */

  /* 주 색상 - Apple Blue 계열 */
  --color-primary: #0071e3;
  --color-primary-light: #0077ed;
  --color-primary-dark: #0051a3;
  --color-primary-rgb: 0, 113, 227;

  /* 배경 색상 */
  --color-background: #fafafa;
  --color-background-gradient: linear-gradient(135deg, #fafafa 0%, #f0f0f5 100%);

  /* 텍스트 색상 */
  --color-text-primary: #1d1d1f;
  --color-text-secondary: #86868b;
  --color-text-tertiary: #6e6e73;

  /* 테두리 & 그림자 */
  --color-border: rgba(0, 0, 0, 0.08);
  --color-shadow: rgba(0, 0, 0, 0.08);

  /* 코드 블록 색상 - VS Code Dark+ 테마 */
  --color-code-background: #1e1e1e;
  --color-code-text: #d4d4d4;
  --color-code-keyword: #569cd6;
  --color-code-string: #ce9178;
  --color-code-comment: #6a9955;
  --color-code-function: #dcdcaa;
  --color-code-number: #b5cea8;
  --color-code-property: #9cdcfe;
  --color-code-operator: #d4d4d4;
  --color-code-tag: #4ec9b0;
  --color-code-attribute: #9cdcfe;

  /* 상태 색상 */
  --color-success: #4caf50;
  --color-warning: #ff9800;
  --color-error: #f44336;
  --color-info: #2196f3;

  /* ==================== 간격 (Spacing) ==================== */

  --spacing-xs: 0.25rem;
  --spacing-sm: 0.5rem;
  --spacing-md: 1rem;
  --spacing-lg: 2rem;
  --spacing-xl: 3rem;
  --spacing-2xl: 4rem;

  /* ==================== 타이포그래피 ==================== */

  --font-family-primary: -apple-system, BlinkMacSystemFont, 'SF Pro Display', 'Segoe UI', 'Roboto', sans-serif;
  --font-family-code: 'SF Mono', 'Fira Code', 'Consolas', 'Monaco', 'Courier New', monospace;

  /* 폰트 크기 */
  --font-size-xs: 0.75rem;
  --font-size-sm: 0.875rem;
  --font-size-base: 1rem;
  --font-size-lg: 1.125rem;
  --font-size-xl: 1.25rem;
  --font-size-2xl: 1.5rem;
  --font-size-3xl: 2rem;
  --font-size-4xl: 2.5rem;
  --font-size-5xl: 3rem;

  /* 폰트 굵기 */
  --font-weight-normal: 400;
  --font-weight-medium: 500;
  --font-weight-semibold: 600;
  --font-weight-bold: 700;
  --font-weight-extrabold: 800;

  /* 줄 간격 */
  --line-height-tight: 1.25;
  --line-height-normal: 1.5;
  --line-height-relaxed: 1.75;
  --line-height-loose: 2;

  /* ==================== 레이아웃 ==================== */

  --layout-sidebar-width: 300px;
  --layout-content-max-width: 900px;
  --layout-container-padding: 2rem;

  /* ==================== Border Radius ==================== */

  --border-radius-sm: 8px;
  --border-radius-md: 12px;
  --border-radius-lg: 16px;
  --border-radius-xl: 20px;
  --border-radius-full: 9999px;

  /* ==================== 애니메이션 ==================== */

  --transition-duration-fast: 150ms;
  --transition-duration-normal: 300ms;
  --transition-duration-slow: 500ms;

  --transition-timing-ease: cubic-bezier(0.4, 0, 0.2, 1);
  --transition-timing-ease-in: cubic-bezier(0.4, 0, 1, 1);
  --transition-timing-ease-out: cubic-bezier(0, 0, 0.2, 1);
  --transition-timing-ease-in-out: cubic-bezier(0.4, 0, 0.2, 1);

  --transition-all-fast: all var(--transition-duration-fast) var(--transition-timing-ease-out);
  --transition-all-normal: all var(--transition-duration-normal) var(--transition-timing-ease);
  --transition-all-slow: all var(--transition-duration-slow) var(--transition-timing-ease);

  /* ==================== Z-Index ==================== */

  --z-index-dropdown: 1000;
  --z-index-sticky: 1020;
  --z-index-fixed: 1030;
  --z-index-modal-backdrop: 1040;
  --z-index-modal: 1050;
  --z-index-popover: 1060;
  --z-index-tooltip: 1070;

  /* ==================== 그림자 (Shadows) ==================== */

  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
  --shadow-2xl: 0 25px 50px -12px rgba(0, 0, 0, 0.25);

  /* ==================== 호환성 레거시 변수 ==================== */

  --primary: var(--color-primary);
  --primary-light: var(--color-primary-light);
  --primary-dark: var(--color-primary-dark);
  --bg: var(--color-background);
  --bg-gradient: var(--color-background-gradient);
  --text: var(--color-text-primary);
  --text-secondary: var(--color-text-secondary);
  --border: var(--color-border);
  --shadow: var(--color-shadow);
  --code-bg: var(--color-code-background);
  --code-text: var(--color-code-text);
  --code-keyword: var(--color-code-keyword);
  --code-string: var(--color-code-string);
  --code-comment: var(--color-code-comment);
  --code-function: var(--color-code-function);
  --code-number: var(--color-code-number);
  --code-property: var(--color-code-property);
  --code-operator: var(--color-code-operator);
  --code-tag: var(--color-code-tag);
  --code-attribute: var(--color-code-attribute);

  --s: var(--spacing-sm);
  --m: var(--spacing-md);
  --l: var(--spacing-lg);
  --xl: var(--spacing-xl);

  --font: var(--font-family-primary);
  --mono: var(--font-family-code);

  --sidebar: var(--layout-sidebar-width);
  --max: var(--layout-content-max-width);

  --radius: var(--border-radius-lg);
  --radius-sm: var(--border-radius-sm);

  --transition: var(--transition-all-normal);
  --transition-fast: var(--transition-all-fast);
}

/* ============================================
   다크모드 자동 대응
   ============================================ */

@media (prefers-color-scheme: dark) {
  :root {
    --color-background: #000000;
    --color-background-gradient: linear-gradient(135deg, #000000 0%, #1a1a1a 100%);
    --color-text-primary: #f5f5f7;
    --color-text-secondary: #86868b;
    --color-text-tertiary: #a1a1a6;
    --color-border: rgba(255, 255, 255, 0.1);
    --color-shadow: rgba(0, 0, 0, 0.4);
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.5);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.6);
    --shadow-2xl: 0 25px 50px -12px rgba(0, 0, 0, 0.7);
  }
}

/* ============================================
   레이아웃
   ============================================ */

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  scroll-padding-top: 80px;
}

body {
  font-family: var(--font);
  color: var(--text);
  background: var(--bg-gradient);
  background-attachment: fixed;
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

.container {
  display: flex;
  min-height: 100vh;
}

/* 사이드바 - 글래스모피즘 */
.sidebar {
  width: var(--sidebar);
  padding: var(--l);
  position: sticky;
  top: 0;
  height: 100vh;
  overflow-y: auto;
  overflow-x: hidden;
  background: rgba(255, 255, 255, 0.7);
  backdrop-filter: blur(20px) saturate(180%);
  -webkit-backdrop-filter: blur(20px) saturate(180%);
  border-right: 1px solid var(--border);
  box-shadow: 2px 0 20px var(--shadow);
  transition: transform 0.4s var(--transition-timing-ease);
}

/* 데스크톱에서 사이드바 숨기기 */
@media (min-width: 768px) {
  .sidebar.active {
    transform: translateX(-100%);
  }
}

@media (prefers-color-scheme: dark) {
  .sidebar {
    background: rgba(30, 30, 30, 0.8);
  }
}

.sidebar h2 {
  font-size: 1.5em;
  margin-bottom: var(--l);
  font-weight: 700;
  background: linear-gradient(135deg, var(--primary), var(--primary-light));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

/* 메인 콘텐츠 */
main {
  flex: 1;
  padding: var(--xl) var(--l);
  max-width: var(--max);
  margin: 0 auto;
  width: 100%;
}

/* 스크롤바 */
.sidebar::-webkit-scrollbar {
  width: 8px;
}

.sidebar::-webkit-scrollbar-track {
  background: transparent;
}

.sidebar::-webkit-scrollbar-thumb {
  background: rgba(0, 0, 0, 0.2);
  border-radius: 10px;
}

.sidebar::-webkit-scrollbar-thumb:hover {
  background: rgba(0, 0, 0, 0.3);
}

@media (prefers-color-scheme: dark) {
  .sidebar::-webkit-scrollbar-thumb {
    background: rgba(255, 255, 255, 0.2);
  }

  .sidebar::-webkit-scrollbar-thumb:hover {
    background: rgba(255, 255, 255, 0.3);
  }
}

/* ============================================
   네비게이션 컴포넌트
   ============================================ */

details {
  margin-bottom: var(--s);
  border-radius: var(--radius-sm);
  transition: background 0.2s ease;
}

details[open] {
  background: rgba(0, 113, 227, 0.05);
}

summary {
  padding: var(--m);
  cursor: pointer;
  font-weight: 600;
  font-size: 0.95em;
  user-select: none;
  border-radius: var(--radius-sm);
  transition: background 0.2s ease;
  list-style: none;
  display: flex;
  align-items: center;
  gap: var(--s);
}

summary::-webkit-details-marker {
  display: none;
}

summary .fa-chevron-right {
  display: inline-block;
  transition: transform 0.2s ease;
  color: var(--primary);
  font-size: 0.8em;
  margin-right: var(--s);
}

details[open] summary .fa-chevron-right {
  transform: rotate(90deg);
}

summary:hover {
  background: rgba(0, 113, 227, 0.08);
}

/* 사이드바 링크 */
.sidebar a {
  display: block;
  padding: var(--s) var(--m);
  padding-left: calc(var(--m) * 2);
  color: var(--text);
  text-decoration: none;
  border-radius: var(--radius-sm);
  transition: background 0.2s ease, color 0.2s ease;
  font-size: 0.9em;
  position: relative;
}

.sidebar a::before {
  content: '';
  position: absolute;
  left: var(--m);
  top: 50%;
  transform: translateY(-50%);
  width: 4px;
  height: 4px;
  background: var(--text-secondary);
  border-radius: 50%;
  transition: background 0.2s ease;
}

.sidebar a:hover {
  background: rgba(0, 113, 227, 0.1);
  color: var(--primary);
}

.sidebar a:hover::before {
  background: var(--primary);
}

/* ============================================
   타이포그래피
   ============================================ */

h1 {
  font-size: 3em;
  margin-bottom: var(--l);
  font-weight: 800;
  color: var(--text);
  letter-spacing: -1px;
  line-height: 1.2;
  display: flex;
  align-items: center;
  gap: var(--m);
}

h1 i {
  color: var(--primary);
}

h2 {
  font-size: 2em;
  margin: calc(var(--l) * 2) 0 var(--l);
  font-weight: 700;
  color: var(--text);
  position: relative;
  padding-bottom: var(--m);
  letter-spacing: -0.5px;
  transition: color 0.2s ease;
}

h2:hover {
  color: var(--primary);
}

h2::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 60px;
  height: 3px;
  background: var(--primary);
  border-radius: 2px;
  transition: width 0.2s ease;
}

h2:hover::after {
  width: 30%;
}

h3 {
  font-size: 1.5em;
  margin: var(--xl) 0 var(--m);
  font-weight: 800;
  color: var(--text);
  letter-spacing: -0.3px;
}

p {
  margin-bottom: var(--l);
  line-height: 1.9;
  color: var(--text);
  font-size: 1.05em;
}

strong {
  font-weight: 700;
  color: var(--primary);
}

em {
  font-style: normal;
  color: var(--primary);
  font-weight: 600;
  background: rgba(0, 113, 227, 0.1);
  padding: 2px 6px;
  border-radius: 4px;
}

mark {
  background: rgba(255, 235, 59, 0.3);
  padding: 3px 6px;
  border-radius: 4px;
  color: var(--text);
}

/* 메인 영역 링크 */
main a {
  color: var(--primary);
  text-decoration: none;
  border-bottom: 2px solid transparent;
  transition: border-color 0.2s ease;
  display: inline;
  padding: 0;
}

main a:hover {
  border-bottom-color: var(--primary);
}

hr {
  border: none;
  height: 2px;
  background: linear-gradient(90deg, transparent, var(--border), transparent);
  margin: calc(var(--l) * 3) 0;
}

blockquote {
  margin: var(--l) 0;
  padding: var(--l);
  border-left: 4px solid var(--primary);
  background: rgba(0, 113, 227, 0.05);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  font-style: normal;
  color: var(--text);
}

::selection {
  background: rgba(0, 113, 227, 0.25);
  color: var(--text);
}

/* ============================================
   콘텐츠 섹션
   ============================================ */

.content-section {
  margin-bottom: var(--xl);
  padding: var(--l);
  background: rgba(255, 255, 255, 0.6);
  backdrop-filter: blur(10px);
  border-radius: var(--radius);
  border: 1px solid var(--border);
  box-shadow: 0 4px 16px var(--shadow);
  transition: box-shadow 0.2s ease, transform 0.2s ease;
}

.content-section:hover {
  box-shadow: 0 8px 24px var(--shadow);
  transform: translateY(-2px);
}

@media (prefers-color-scheme: dark) {
  .content-section {
    background: rgba(30, 30, 30, 0.6);
  }
}

/* ============================================
   코드 블록
   ============================================ */

.code-block {
  background: var(--code-bg);
  padding: var(--l);
  border-radius: var(--radius);
  overflow-x: auto;
  margin: var(--l) 0;
  border: none;
  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.3);
  position: relative;
}

.code-block pre {
  margin: 0;
  color: var(--code-text);
  line-height: 1.8;
  font-size: 0.95em;
  border: none !important;
  outline: none !important;
}

.code-block code {
  font-family: var(--mono);
  color: var(--code-text);
  font-weight: 400;
  border: none !important;
  outline: none !important;
  background: none !important;
}

/* Syntax Highlighting */
.code-block .comment { color: var(--code-comment); }
.code-block .keyword { color: var(--code-keyword); font-weight: 500; }
.code-block .string { color: var(--code-string); }
.code-block .number { color: var(--code-number); }
.code-block .function { color: var(--code-function); font-weight: 500; }
.code-block .property { color: var(--code-property); }
.code-block .tag { color: var(--code-tag); }
.code-block .attr { color: var(--code-attribute); }
.code-block .operator { color: var(--code-operator); }

/* 인라인 코드 */
code {
  background: rgba(0, 113, 227, 0.1);
  color: var(--primary-dark);
  padding: 4px 8px;
  border-radius: 6px;
  font-family: var(--mono);
  font-size: 0.9em;
  border: 1px solid rgba(0, 113, 227, 0.15);
  font-weight: 500;
}

/* 스크롤바 */
.code-block::-webkit-scrollbar {
  height: 10px;
}

.code-block::-webkit-scrollbar-track {
  background: rgba(255, 255, 255, 0.05);
  border-radius: 5px;
}

.code-block::-webkit-scrollbar-thumb {
  background: rgba(255, 255, 255, 0.2);
  border-radius: 5px;
}

.code-block::-webkit-scrollbar-thumb:hover {
  background: rgba(255, 255, 255, 0.3);
}

/* ============================================
   리스트
   ============================================ */

ul, ol {
  margin: var(--m) 0 calc(var(--l) * 1.2);
  padding-left: var(--l);
}

ul li {
  list-style: none;
  position: relative;
  padding-left: var(--s);
  margin-bottom: var(--s);
  line-height: 1.6;
}

ul li::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0.65em;
  width: 3px;
  height: 3px;
  background: var(--primary);
  border-radius: 50%;
}

ol li {
  margin-bottom: var(--m);
  line-height: 1.8;
}

/* ============================================
   테이블
   ============================================ */

table {
  width: 100%;
  border-collapse: separate;
  border-spacing: 0;
  margin: var(--l) 0;
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: 0 4px 16px var(--shadow);
}

th, td {
  padding: var(--m) var(--l);
  text-align: left;
  border-bottom: 1px solid var(--border);
}

th {
  background: rgba(0, 113, 227, 0.1);
  font-weight: 600;
  color: var(--primary-dark);
}

tr:hover {
  background: rgba(0, 113, 227, 0.03);
}

tr:last-child td {
  border-bottom: none;
}

/* ============================================
   강조 박스
   ============================================ */

/* 정보/팁/경고 박스 - 확실하게 눈에 띄게! */
.tip, .warning, .info {
  padding: calc(var(--m));
  margin: calc(var(--xl) * 1.5) 0;
  border-radius: var(--radius);
  border: 3px solid;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.15);
  font-size: 0.9em;
  font-weight: 700;
  line-height: 1.9;
  position: relative;
  overflow: hidden;
}

/* 왼쪽 강조 바 */
.tip::before, .warning::before, .info::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  bottom: 0;
  width: 8px;
}

/* 정보 박스 (파란색) */
.info {
  background: linear-gradient(135deg,
    rgba(59, 130, 246, 0.25) 0%,
    rgba(59, 130, 246, 0.15) 50%,
    rgba(59, 130, 246, 0.1) 100%
  );
  border-color: #3b82f6;
  color: var(--text);
}

.info::before {
  background: linear-gradient(180deg, #3b82f6, #2563eb);
}

.info strong {
  color: #1e40af;
  font-weight: 800;
  font-size: 1.15em;
}

.info i {
  color: #3b82f6;
  margin-right: var(--s);
  font-size: 1.3em;
}

/* 팁 박스 (초록색) */
.tip {
  background: linear-gradient(135deg,
    rgba(16, 185, 129, 0.25) 0%,
    rgba(16, 185, 129, 0.15) 50%,
    rgba(16, 185, 129, 0.1) 100%
  );
  border-color: #10b981;
  color: var(--text);
}

.tip::before {
  background: linear-gradient(180deg, #10b981, #059669);
}

.tip strong {
  color: #065f46;
  font-weight: 800;
  font-size: 1.15em;
}

.tip i {
  color: #10b981;
  margin-right: var(--s);
  font-size: 1.3em;
}

/* 경고 박스 (노란색/주황색) */
.warning {
  background: linear-gradient(135deg,
    rgba(251, 146, 60, 0.25) 0%,
    rgba(251, 146, 60, 0.15) 50%,
    rgba(251, 146, 60, 0.1) 100%
  );
  border-color: #fb923c;
  color: var(--text);
}

.warning::before {
  background: linear-gradient(180deg, #fb923c, #ea580c);
}

.warning strong {
  color: #9a3412;
  font-weight: 800;
  font-size: 1.15em;
}

.warning i {
  color: #fb923c;
  margin-right: var(--s);
  font-size: 1.3em;
}

/* 박스 내부 요소 스타일 */
.tip p, .warning p, .info p {
  margin-bottom: var(--m);
  line-height: 1.9;
}

.tip p:last-child, .warning p:last-child, .info p:last-child {
  margin-bottom: 0;
}

.tip ul, .warning ul, .info ul {
  margin-top: var(--m);
  margin-bottom: var(--m);
}

.tip li, .warning li, .info li {
  margin-bottom: var(--s);
}

/* 박스 내부 코드 */
.tip code, .warning code, .info code {
  background: rgba(0, 0, 0, 0.1);
  border: 1px solid rgba(0, 0, 0, 0.2);
  font-weight: 600;
}

/* 다크모드 대응 */
@media (prefers-color-scheme: dark) {
  .tip, .warning, .info {
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.4);
  }

  .tip code, .warning code, .info code {
    background: rgba(255, 255, 255, 0.15);
    border-color: rgba(255, 255, 255, 0.25);
  }
}

/* ============================================
   예제 박스
   ============================================ */

.example {
  border: 2px solid var(--border);
  padding: var(--l);
  margin: var(--l) 0;
  border-radius: var(--radius);
  background: rgba(255, 255, 255, 0.5);
  box-shadow: 0 2px 12px var(--shadow);
}

@media (prefers-color-scheme: dark) {
  .example {
    background: rgba(30, 30, 30, 0.5);
  }
}

/* ============================================
   이미지
   ============================================ */

img {
  max-width: 100%;
  height: auto;
  border-radius: var(--radius);
  box-shadow: 0 4px 16px var(--shadow);
  transition: transform 0.2s ease;
}

img:hover {
  transform: translateY(-2px);
}

/* ============================================
   배지 & 카드
   ============================================ */

.badge {
  display: inline-block;
  padding: 4px 12px;
  background: var(--primary);
  color: white;
  border-radius: 20px;
  font-size: 0.85em;
  font-weight: 600;
  margin: 0 4px;
}

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: var(--l);
  margin: var(--l) 0;
}

.card {
  padding: var(--l);
  background: rgba(255, 255, 255, 0.6);
  backdrop-filter: blur(10px);
  border-radius: var(--radius);
  border: 1px solid var(--border);
  box-shadow: 0 4px 16px var(--shadow);
  transition: var(--transition);
}

.card:hover {
  transform: translateY(-4px);
  box-shadow: 0 8px 32px var(--shadow);
}

@media (prefers-color-scheme: dark) {
  .card {
    background: rgba(30, 30, 30, 0.6);
  }
}

/* ============================================
   Font Awesome 아이콘
   ============================================ */

h1 i, h2 i, h3 i {
  margin-right: var(--s);
}

h2 i {
  color: var(--primary);
  font-size: 0.9em;
}

h3 i {
  color: var(--primary-light);
  font-size: 0.9em;
}

.sidebar summary i {
  margin-right: var(--s);
  font-size: 1em;
  color: var(--primary);
}

.tip i, .warning i, .info i {
  margin-right: var(--s);
  font-size: 1.2em;
}

.tip i { color: #10b981; }
.warning i { color: #fbbf24; padding-left: var(--m);}
.info i { color: var(--primary); }

summary:hover i {
  transform: scale(1.1);
  transition: transform 0.2s ease;
}

/* ============================================
   Prism.js 코드 하이라이팅
   ============================================ */

code[class*="language-"],
pre[class*="language-"] {
  color: var(--color-code-text);
  background: none;
  font-family: var(--mono);
  font-size: 0.95em;
  text-align: left;
  white-space: pre;
  word-spacing: normal;
  word-break: normal;
  word-wrap: normal;
  line-height: 1.8;
  tab-size: 4;
  hyphens: none;
  border: none !important;
  outline: none !important;
}

pre[class*="language-"] {
  padding: 0;
  margin: 0;
  overflow: auto;
  border: none !important;
  outline: none !important;
}

:not(pre) > code[class*="language-"],
pre[class*="language-"] {
  background: var(--color-code-background);
  border: none !important;
  outline: none !important;
}

:not(pre) > code[class*="language-"] {
  padding: 0.1em;
  border-radius: 0.3em;
  white-space: normal;
}

/* ============================================
   햄버거 메뉴 (고정)
   ============================================ */

.hamburger-btn {
  position: fixed;
  top: 20px;
  right: 20px;
  z-index: calc(var(--z-index-fixed) + 1);
  width: 44px;
  height: 44px;
  background: linear-gradient(135deg, var(--primary) 0%, var(--primary-light) 100%);
  border: none;
  border-radius: 14px;
  cursor: pointer;
  display: none;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  gap: 6px;
  box-shadow: 0 4px 20px rgba(var(--color-primary-rgb), 0.4);
  transition: all 0.3s var(--transition-timing-ease);
}

.hamburger-btn:hover {
  transform: translateY(-3px);
  box-shadow: 0 8px 25px rgba(var(--color-primary-rgb), 0.5);
}

.hamburger-btn:active {
  transform: translateY(-1px);
}

.hamburger-btn span {
  width: 16px;
  height: 2px;
  background: white;
  border-radius: 3px;
  transition: all 0.3s var(--transition-timing-ease);
}

.hamburger-btn.active span:nth-child(1) {
  transform: rotate(45deg) translate(9px, 9px);
}

.hamburger-btn.active span:nth-child(2) {
  opacity: 0;
  transform: translateX(20px);
}

.hamburger-btn.active span:nth-child(3) {
  transform: rotate(-45deg) translate(9px, -9px);
}

/* 오버레이 */
.overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: rgba(0, 0, 0, 0.6);
  z-index: calc(var(--z-index-fixed) - 1);
  opacity: 0;
  visibility: hidden;
  transition: all 0.3s var(--transition-timing-ease);
  backdrop-filter: blur(4px);
  -webkit-backdrop-filter: blur(4px);
}

.overlay.active {
  opacity: 1;
  visibility: visible;
}


/* ============================================
   애니메이션
   ============================================ */

@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes slideIn {
  from {
    opacity: 0;
    transform: translateX(-20px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

.content-section {
  animation: fadeInUp 0.6s cubic-bezier(0.4, 0, 0.2, 1);
}

.sidebar details {
  animation: slideIn 0.3s ease-out;
}

:focus-visible {
  outline: 3px solid var(--primary);
  outline-offset: 3px;
  border-radius: var(--radius-sm);
}

/* ============================================
   반응형 다이어그램 시각화
   ============================================ */

/* 디바이스 진열 */
.device-showcase {
  display: flex;
  align-items: flex-end;
  justify-content: center;
  gap: 28px;
  padding: 28px 20px 20px;
  background: linear-gradient(135deg, rgba(0,113,227,0.06), rgba(0,113,227,0.02));
  border-radius: var(--radius);
  border: 1px solid var(--border);
  margin: var(--l) 0;
  flex-wrap: wrap;
}

.device-frame {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
}

.device-name {
  font-size: 0.8em;
  font-weight: 700;
  color: var(--text-secondary);
  text-align: center;
}

.device-px {
  font-size: 0.7em;
  color: var(--text-secondary);
  text-align: center;
  margin-top: -4px;
}

/* 폰 목업 */
.mock-phone {
  width: 72px;
  height: 128px;
  border: 3px solid #374151;
  border-radius: 14px;
  background: #f3f4f6;
  padding: 16px 5px 22px;
  box-shadow: 0 6px 18px rgba(0,0,0,0.15);
  overflow: hidden;
  position: relative;
}

.mock-phone::before {
  content: '';
  position: absolute;
  top: 7px;
  left: 50%;
  transform: translateX(-50%);
  width: 16px;
  height: 3px;
  background: #9ca3af;
  border-radius: 2px;
}

.mock-phone::after {
  content: '';
  position: absolute;
  bottom: 7px;
  left: 50%;
  transform: translateX(-50%);
  width: 18px;
  height: 18px;
  border: 2px solid #9ca3af;
  border-radius: 50%;
}

/* 태블릿 목업 */
.mock-tablet {
  width: 110px;
  height: 148px;
  border: 3px solid #374151;
  border-radius: 10px;
  background: #f3f4f6;
  padding: 8px 5px 22px;
  box-shadow: 0 6px 18px rgba(0,0,0,0.15);
  overflow: hidden;
  position: relative;
}

.mock-tablet::after {
  content: '';
  position: absolute;
  bottom: 5px;
  left: 50%;
  transform: translateX(-50%);
  width: 14px;
  height: 14px;
  border: 2px solid #9ca3af;
  border-radius: 50%;
}

/* 데스크톱 목업 */
.mock-desktop {
  width: 188px;
  height: 118px;
  border: 3px solid #374151;
  border-radius: 8px 8px 0 0;
  background: #f3f4f6;
  padding: 5px;
  box-shadow: 0 6px 18px rgba(0,0,0,0.15);
  overflow: hidden;
}

.mock-stand {
  width: 48px;
  height: 14px;
  background: #374151;
  border-radius: 0 0 2px 2px;
  margin: 0 auto;
}

.mock-foot {
  width: 76px;
  height: 5px;
  background: #4b5563;
  border-radius: 3px;
  margin: 0 auto;
}

/* 화면 내부 레이아웃 */
.mock-screen {
  height: 100%;
  display: flex;
  flex-direction: column;
  gap: 3px;
}

.mock-topbar {
  height: 8px;
  background: var(--primary);
  border-radius: 2px;
  flex-shrink: 0;
}

.mock-body {
  flex: 1;
  display: flex;
  gap: 3px;
  overflow: hidden;
}

.mock-col {
  flex: 1;
  background: rgba(0,113,227,0.25);
  border-radius: 2px;
}

.mock-col-sm {
  flex: 0.55;
  background: rgba(0,113,227,0.15);
  border-radius: 2px;
}

.mock-col-lg {
  flex: 1.8;
  background: rgba(0,113,227,0.3);
  border-radius: 2px;
}

.mock-footer {
  height: 5px;
  background: rgba(0,113,227,0.12);
  border-radius: 2px;
  flex-shrink: 0;
}

/* 브레이크포인트 시각화 */
.bp-viz {
  margin: var(--l) 0;
  padding: 20px;
  background: rgba(0,0,0,0.03);
  border-radius: var(--radius);
  border: 1px solid var(--border);
}

.bp-viz-title {
  font-size: 0.82em;
  font-weight: 700;
  color: var(--text-secondary);
  margin-bottom: 12px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.bp-bar {
  height: 40px;
  border-radius: 8px;
  overflow: hidden;
  display: flex;
}

.bp-seg {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.7em;
  font-weight: 700;
  color: white;
  text-shadow: 0 1px 3px rgba(0,0,0,0.25);
  min-width: 0;
  overflow: hidden;
}

.bp-seg.bp-mobile  { background: #10b981; flex: 3; }
.bp-seg.bp-tablet  { background: #0071e3; flex: 2.5; }
.bp-seg.bp-desktop { background: #8b5cf6; flex: 2; }
.bp-seg.bp-wide    { background: #f59e0b; flex: 1.5; }

.bp-legend {
  display: flex;
  gap: 16px;
  margin-top: 12px;
  flex-wrap: wrap;
}

.bp-legend-item {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 0.78em;
  font-weight: 600;
  color: var(--text-secondary);
}

.bp-dot {
  width: 10px;
  height: 10px;
  border-radius: 3px;
  flex-shrink: 0;
}

/* 레이아웃 열 변화 시각화 */
.layout-evo {
  margin: var(--l) 0;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.layout-step {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 10px 14px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
  background: rgba(255,255,255,0.5);
}

.step-badge {
  font-size: 0.72em;
  font-weight: 800;
  padding: 4px 10px;
  border-radius: 20px;
  white-space: nowrap;
  min-width: 90px;
  text-align: center;
  flex-shrink: 0;
}

.step-badge.mobile  { background: rgba(16,185,129,0.15); color: #059669; }
.step-badge.tablet  { background: rgba(0,113,227,0.15);  color: #0051a3; }
.step-badge.desktop { background: rgba(139,92,246,0.15); color: #6d28d9; }
.step-badge.wide    { background: rgba(245,158,11,0.15); color: #d97706; }

.step-cols {
  display: flex;
  gap: 5px;
  flex: 1;
  height: 38px;
}

.step-col {
  flex: 1;
  border-radius: 4px;
  border: 1.5px solid rgba(0,113,227,0.35);
  background: linear-gradient(135deg, rgba(0,113,227,0.22), rgba(0,113,227,0.1));
}

.step-desc {
  font-size: 0.78em;
  color: var(--text-secondary);
  min-width: 60px;
  text-align: right;
  flex-shrink: 0;
}

/* 접근법 비교 카드 */
.approach-compare {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin: var(--l) 0;
}

.approach-card {
  padding: 16px;
  border-radius: var(--radius-sm);
  border: 2px solid;
}

.approach-card.mobile-first {
  border-color: #10b981;
  background: rgba(16,185,129,0.05);
}

.approach-card.desktop-first {
  border-color: #f59e0b;
  background: rgba(245,158,11,0.05);
}

.approach-title {
  font-size: 0.85em;
  font-weight: 800;
  margin-bottom: 10px;
}

.approach-title.green  { color: #059669; }
.approach-title.orange { color: #d97706; }

.approach-flow {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.flow-item {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 0.75em;
}

.flow-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  flex-shrink: 0;
}

.flow-dot.green  { background: #10b981; }
.flow-dot.blue   { background: #0071e3; }
.flow-dot.purple { background: #8b5cf6; }

.flow-line {
  width: 1px;
  height: 8px;
  background: var(--border);
  margin-left: 3.5px;
}

.flow-label {
  color: var(--text-secondary);
  font-weight: 600;
}

.flow-query {
  font-family: var(--mono);
  font-size: 0.85em;
  color: var(--primary-dark);
  background: rgba(0,113,227,0.1);
  padding: 1px 5px;
  border-radius: 4px;
}

/* 프로젝트 시각화 - mock 내부 레이아웃 */
.mock-cards {
  display: flex;
  flex-wrap: wrap;
  gap: 2px;
  padding: 2px;
  align-content: flex-start;
}

.mock-card-item {
  flex: 1 1 45%;
  height: 18px;
  background: rgba(0,113,227,0.22);
  border-radius: 2px;
}

.mock-card-full {
  flex: 1 1 100%;
  height: 8px;
  background: rgba(0,113,227,0.12);
  border-radius: 2px;
}

.mock-sidebar-layout {
  display: flex;
  gap: 2px;
  height: 100%;
}

.mock-nav-side {
  width: 28%;
  background: rgba(0,113,227,0.2);
  border-radius: 2px;
  display: flex;
  flex-direction: column;
  gap: 2px;
  padding: 3px 2px;
}

.mock-nav-link {
  height: 6px;
  background: rgba(0,113,227,0.4);
  border-radius: 1px;
}

.mock-content-main {
  flex: 1;
  background: rgba(0,113,227,0.07);
  border-radius: 2px;
  display: flex;
  flex-direction: column;
  gap: 2px;
  padding: 2px;
}

.mock-text-line {
  height: 4px;
  background: rgba(0,113,227,0.18);
  border-radius: 2px;
}

.mock-text-line.short { width: 60%; }
.mock-text-line.med { width: 80%; }

/* CSS 단위 비교 */
.unit-compare {
  padding: 20px;
  background: rgba(0,0,0,0.03);
  border-radius: var(--radius);
  border: 1px solid var(--border);
  margin: var(--l) 0;
}

.unit-compare-title {
  font-size: 0.78em;
  font-weight: 700;
  color: var(--text-secondary);
  margin-bottom: 14px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.unit-row {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 8px;
}

.unit-label {
  font-family: var(--mono);
  font-weight: 800;
  font-size: 0.78em;
  color: var(--primary-dark);
  min-width: 36px;
  text-align: right;
}

.unit-bar {
  height: 26px;
  border-radius: 5px;
  display: flex;
  align-items: center;
  padding: 0 10px;
  font-size: 0.68em;
  font-weight: 700;
  color: white;
  white-space: nowrap;
  min-width: 20px;
}

.unit-note {
  font-size: 0.7em;
  color: var(--text-secondary);
  flex: 1;
}

/* Grid Named Areas 시각화 */
.grid-named-compare {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin: var(--l) 0;
}

.grid-named-box {
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  overflow: hidden;
}

.grid-named-title {
  padding: 8px 12px;
  font-size: 0.75em;
  font-weight: 700;
  background: rgba(0,0,0,0.04);
  border-bottom: 1px solid var(--border);
  color: var(--text-secondary);
}

.grid-viz-desktop {
  display: grid;
  grid-template-areas: "h h h" "s m m" "f f f";
  grid-template-columns: 80px 1fr 1fr;
  grid-template-rows: 30px 90px 26px;
  gap: 3px;
  padding: 4px;
  background: rgba(0,0,0,0.03);
}

.grid-viz-mobile {
  display: grid;
  grid-template-areas: "h" "m" "s" "f";
  grid-template-rows: 26px 60px 40px 22px;
  gap: 3px;
  padding: 4px;
  background: rgba(0,0,0,0.03);
}

.gv-h { grid-area: h; background: var(--primary); display: flex; align-items: center; justify-content: center; color: white; font-size: 0.66em; font-weight: 700; border-radius: 2px; }
.gv-s { grid-area: s; background: rgba(0,113,227,0.25); display: flex; align-items: center; justify-content: center; font-size: 0.64em; font-weight: 600; color: #0051a3; border-radius: 2px; }
.gv-m { grid-area: m; background: rgba(0,113,227,0.1); display: flex; align-items: center; justify-content: center; font-size: 0.64em; color: var(--text-secondary); border-radius: 2px; }
.gv-f { grid-area: f; background: rgba(0,0,0,0.08); display: flex; align-items: center; justify-content: center; font-size: 0.62em; color: var(--text-secondary); border-radius: 2px; }

/* Auto-fill vs Auto-fit 비교 */
.autofill-compare {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin: var(--l) 0;
}

.autofill-box {
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  overflow: hidden;
}

.autofill-label {
  padding: 8px 12px;
  font-size: 0.72em;
  font-weight: 700;
  background: rgba(0,0,0,0.04);
  border-bottom: 1px solid var(--border);
  font-family: var(--mono);
  color: var(--text-secondary);
}

.autofill-content {
  padding: 8px;
}

.autofill-grid-fill {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(36px, 1fr));
  gap: 4px;
}

.autofill-grid-fit {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(36px, 1fr));
  gap: 4px;
}

.autofill-item {
  height: 28px;
  background: rgba(0,113,227,0.2);
  border: 1px solid rgba(0,113,227,0.35);
  border-radius: 3px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.6em;
  font-weight: 700;
  color: #0051a3;
}

/* 전후(Before/After) 비교 */
.before-after {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin: var(--l) 0;
}

.ba-bad {
  border: 2px solid #ef4444;
  border-radius: var(--radius-sm);
  overflow: hidden;
}

.ba-good {
  border: 2px solid #10b981;
  border-radius: var(--radius-sm);
  overflow: hidden;
}

.ba-label {
  padding: 7px 12px;
  font-size: 0.75em;
  font-weight: 800;
}

.ba-bad .ba-label { background: rgba(239,68,68,0.1); color: #dc2626; }
.ba-good .ba-label { background: rgba(16,185,129,0.1); color: #059669; }

.ba-content {
  padding: 12px;
  font-size: 0.78em;
  color: var(--text-secondary);
  min-height: 55px;
  line-height: 1.6;
}

/* 버그 케이스 카드 */
.bug-cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 14px;
  margin: var(--l) 0;
}

.bug-card {
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  overflow: hidden;
}

.bug-card-title {
  padding: 10px 14px;
  font-size: 0.8em;
  font-weight: 800;
  background: rgba(239,68,68,0.08);
  border-bottom: 1px solid var(--border);
  color: #dc2626;
  display: flex;
  align-items: center;
  gap: 6px;
}

.bug-card-body {
  padding: 12px 14px;
  font-size: 0.78em;
  line-height: 1.7;
  color: var(--text-secondary);
}

.bug-fix {
  margin-top: 8px;
  padding: 8px 10px;
  background: rgba(16,185,129,0.08);
  border-radius: 6px;
  border-left: 3px solid #10b981;
  font-size: 0.95em;
  color: var(--text);
}

/* Container Query 시각화 */
.cq-compare {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin: var(--l) 0;
}

.cq-box {
  padding: 14px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: rgba(0,0,0,0.02);
}

.cq-title {
  font-size: 0.78em;
  font-weight: 800;
  margin-bottom: 10px;
  color: var(--text-secondary);
}

.cq-container-wide {
  border: 2px dashed rgba(139,92,246,0.5);
  border-radius: 6px;
  padding: 6px;
  margin-bottom: 8px;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 4px;
}

.cq-container-narrow {
  border: 2px dashed rgba(139,92,246,0.3);
  border-radius: 6px;
  padding: 6px;
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.cq-card {
  background: rgba(139,92,246,0.15);
  border-radius: 3px;
  padding: 4px;
  font-size: 0.65em;
  font-weight: 700;
  color: #6d28d9;
  text-align: center;
}

.cq-card-h { height: 36px; display: flex; align-items: center; justify-content: center; }
.cq-card-v { height: 50px; display: flex; align-items: center; justify-content: center; }

.cq-label {
  font-size: 0.65em;
  color: rgba(139,92,246,0.7);
  text-align: center;
  margin-top: 4px;
  font-weight: 600;
}

/* 성능 지표 카드 */
.perf-cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 12px;
  margin: var(--l) 0;
}

.perf-card {
  padding: 14px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
  border-top: 3px solid;
}

.perf-card.green { border-top-color: #10b981; }
.perf-card.blue  { border-top-color: #0071e3; }
.perf-card.purple{ border-top-color: #8b5cf6; }

.perf-metric {
  font-size: 0.72em;
  font-weight: 800;
  font-family: var(--mono);
  color: var(--text-secondary);
  margin-bottom: 4px;
}

.perf-name {
  font-size: 0.88em;
  font-weight: 700;
  margin-bottom: 6px;
}

.perf-desc {
  font-size: 0.75em;
  color: var(--text-secondary);
  line-height: 1.5;
}

/* 미디어 쿼리 타입 그리드 */
.mq-types {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 10px;
  margin: var(--l) 0;
}

.mq-type-card {
  padding: 12px 14px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
  background: rgba(255,255,255,0.5);
}

.mq-type-name {
  font-family: var(--mono);
  font-size: 0.78em;
  font-weight: 800;
  color: var(--primary-dark);
  margin-bottom: 4px;
}

.mq-type-desc {
  font-size: 0.73em;
  color: var(--text-secondary);
  line-height: 1.5;
}

/* 반응형 조정 */
@media (max-width: 600px) {
  .mock-desktop { width: 130px; height: 82px; }
  .device-showcase { gap: 16px; padding: 18px 12px 14px; }
  .step-desc { display: none; }
  .approach-compare { grid-template-columns: 1fr; }
  .grid-named-compare { grid-template-columns: 1fr; }
  .autofill-compare { grid-template-columns: 1fr; }
  .before-after { grid-template-columns: 1fr; }
  .cq-compare { grid-template-columns: 1fr; }
}

@media (prefers-color-scheme: dark) {
  .mock-phone, .mock-tablet, .mock-desktop {
    background: #1f2937;
    border-color: #4b5563;
  }
  .layout-step { background: rgba(30,30,30,0.5); }
  .bp-viz { background: rgba(255,255,255,0.03); }
  .approach-card.mobile-first  { background: rgba(16,185,129,0.08); }
  .approach-card.desktop-first { background: rgba(245,158,11,0.08); }
}

/* ============================================
   모바일 반응형
   ============================================ */

@media (max-width: 767px) {
  /* 햄버거 버튼 표시 */
  .hamburger-btn {
    display: flex;
  }

  /* 사이드바를 슬라이드 메뉴로 변경 */
  .sidebar {
    position: fixed;
    left: -100%;
    top: 0;
    width: 85%;
    max-width: 320px;
    height: 100vh;
    z-index: var(--z-index-fixed);
    transition: left 0.4s var(--transition-timing-ease);
    overflow-y: auto;
    display: block;
  }

  .sidebar.active {
    left: auto;
    right: 0;
  }

  main {
    padding: var(--l) var(--m);
    width: 100%;
  }

  h1 {
    font-size: 2em;
  }

  h2 {
    font-size: 1.5em;
  }

  h3 {
    font-size: 1.25em;
  }
}