/* ==========================================================================
   Main Stylesheet: Global Design System & Era Theming
   ========================================================================== */

@import url('https://fonts.googleapis.com/css2?family=Cinzel:wght@600;700;900&family=Chakra+Petch:wght@400;600;700&family=Prompt:wght@300;400;500;600;700&family=Sarabun:ital,wght@0,300;0,400;0,500;0,600;0,700;1,400&display=swap');

:root {
  /* Global Brand & Neutral Colors (Default: Dark Mode) */
  --bg-primary: #0f1115;
  --bg-secondary: #161a22;
  --bg-card: rgba(26, 31, 42, 0.75);
  --bg-card-hover: rgba(35, 42, 56, 0.85);
  --text-main: #e6edf3;
  --text-muted: #8b949e;
  --text-bright: #ffffff;
  --border-color: rgba(240, 246, 252, 0.12);
  --border-glow: rgba(56, 139, 253, 0.35);
  --nav-bg: rgba(15, 17, 21, 0.88);
  --modal-bg: #161b22;
  --tag-bg: rgba(255, 255, 255, 0.08);
  --tag-color: #ffffff;

  /* Card backgrounds for flashcard 3D */
  --card-front-bg: linear-gradient(135deg, #1b2029 0%, #161b22 100%);
  --card-back-bg: linear-gradient(135deg, #1f2937 0%, #111827 100%);

  /* WW1 Vintage Palette */
  --ww1-primary: #c29b72;
  --ww1-secondary: #8b7355;
  --ww1-accent: #d4a373;
  --ww1-dark: #1e1915;
  --ww1-bg-card: rgba(35, 29, 24, 0.85);
  --ww1-border: rgba(194, 155, 114, 0.25);
  --ww1-glow: rgba(194, 155, 114, 0.4);

  /* WW2 Industrial Steel & Alert Palette */
  --ww2-primary: #e63946;
  --ww2-secondary: #457b9d;
  --ww2-accent: #f4a261;
  --ww2-dark: #12161a;
  --ww2-bg-card: rgba(22, 28, 35, 0.85);
  --ww2-border: rgba(230, 57, 70, 0.3);
  --ww2-glow: rgba(230, 57, 70, 0.4);

  /* Cold War CRT & Espionage Palette */
  --coldwar-primary: #00f5d4;
  --coldwar-secondary: #7b2cbf;
  --coldwar-accent: #ff0055;
  --coldwar-dark: #080c10;
  --coldwar-bg-card: rgba(12, 18, 26, 0.85);
  --coldwar-border: rgba(0, 245, 212, 0.25);
  --coldwar-glow: rgba(0, 245, 212, 0.4);

  /* Typography */
  --font-serif: 'Cinzel', serif;
  --font-tech: 'Chakra Petch', sans-serif;
  --font-heading: 'Prompt', sans-serif;
  --font-body: 'Sarabun', sans-serif;

  /* Layout */
  --header-height: 72px;
  --container-max-width: 1200px;
  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --transition-fast: 0.2s ease;
  --transition-normal: 0.35s cubic-bezier(0.16, 1, 0.3, 1);
}

/* ==========================================================================
   Display Theme Overrides: Light Mode & Eye-Care (Sepia / Parchment) Mode
   ========================================================================== */

/* 1. Light Mode (โหมดสว่าง) */
[data-theme="light"] {
  --bg-primary: #f6f8fa;
  --bg-secondary: #ffffff;
  --bg-card: rgba(255, 255, 255, 0.95);
  --bg-card-hover: #ffffff;
  --text-main: #24292f;
  --text-muted: #57606a;
  --text-bright: #090c10;
  --border-color: rgba(31, 35, 40, 0.15);
  --border-glow: rgba(9, 105, 218, 0.25);
  --nav-bg: rgba(246, 248, 250, 0.92);
  --modal-bg: #ffffff;
  --tag-bg: rgba(0, 0, 0, 0.06);
  --tag-color: #24292f;

  --card-front-bg: linear-gradient(135deg, #ffffff 0%, #f6f8fa 100%);
  --card-back-bg: linear-gradient(135deg, #f6f8fa 0%, #ffffff 100%);

  /* WW1 Light Palette */
  --ww1-primary: #8b5a2b;
  --ww1-secondary: #6e4620;
  --ww1-accent: #a46d38;
  --ww1-dark: #fbf9f6;
  --ww1-bg-card: rgba(255, 252, 248, 0.95);
  --ww1-border: rgba(139, 90, 43, 0.25);
  --ww1-glow: rgba(139, 90, 43, 0.25);

  /* WW2 Light Palette */
  --ww2-primary: #cf222e;
  --ww2-secondary: #0969da;
  --ww2-accent: #bc4c00;
  --ww2-dark: #fff8f8;
  --ww2-bg-card: rgba(255, 250, 250, 0.95);
  --ww2-border: rgba(207, 34, 46, 0.25);
  --ww2-glow: rgba(207, 34, 46, 0.25);

  /* Cold War Light Palette */
  --coldwar-primary: #0969da;
  --coldwar-secondary: #8250df;
  --coldwar-accent: #cf222e;
  --coldwar-dark: #f6f8fa;
  --coldwar-bg-card: rgba(246, 250, 254, 0.95);
  --coldwar-border: rgba(9, 105, 218, 0.25);
  --coldwar-glow: rgba(9, 105, 218, 0.25);
}

/* 2. Eye-Care Mode (โหมดถนอมสายตา - วอร์มโทนน้ำตาล-เหลืองนวล อ่อนโยนต่อดวงตา) */
[data-theme="eyecare"] {
  --bg-primary: #f4ebd9;
  --bg-secondary: #ece1cc;
  --bg-card: rgba(248, 241, 230, 0.96);
  --bg-card-hover: #fcf6ec;
  --text-main: #3d3126;
  --text-muted: #73614e;
  --text-bright: #261e16;
  --border-color: rgba(120, 95, 68, 0.22);
  --border-glow: rgba(160, 115, 65, 0.35);
  --nav-bg: rgba(244, 235, 217, 0.94);
  --modal-bg: #f7efe1;
  --tag-bg: rgba(120, 95, 68, 0.12);
  --tag-color: #3d3126;

  --card-front-bg: linear-gradient(135deg, #faf3e6 0%, #f4ead7 100%);
  --card-back-bg: linear-gradient(135deg, #f4ead7 0%, #eee1ca 100%);

  /* WW1 Eye-care Palette */
  --ww1-primary: #875225;
  --ww1-secondary: #6e411b;
  --ww1-accent: #9e6330;
  --ww1-dark: #ede1cb;
  --ww1-bg-card: rgba(247, 239, 226, 0.96);
  --ww1-border: rgba(135, 82, 37, 0.28);
  --ww1-glow: rgba(135, 82, 37, 0.3);

  /* WW2 Eye-care Palette */
  --ww2-primary: #b3262e;
  --ww2-secondary: #30658a;
  --ww2-accent: #a35017;
  --ww2-dark: #f0e3d2;
  --ww2-bg-card: rgba(250, 238, 234, 0.96);
  --ww2-border: rgba(179, 38, 46, 0.26);
  --ww2-glow: rgba(179, 38, 46, 0.25);

  /* Cold War Eye-care Palette */
  --coldwar-primary: #15735c;
  --coldwar-secondary: #6b3e94;
  --coldwar-accent: #b3262e;
  --coldwar-dark: #e8ded0;
  --coldwar-bg-card: rgba(238, 245, 239, 0.96);
  --coldwar-border: rgba(21, 115, 92, 0.26);
  --coldwar-glow: rgba(21, 115, 92, 0.25);
}

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

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  background-color: var(--bg-primary);
  color: var(--text-main);
  font-family: var(--font-body);
  line-height: 1.7;
  overflow-x: hidden;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  transition: background-color var(--transition-normal), color var(--transition-normal);
}

/* Background Atmosphere Grid */
.bg-atmosphere {
  position: fixed;
  top: 0;
  left: 0;
  width: 100vw;
  height: 100vh;
  pointer-events: none;
  z-index: -1;
  background: 
    radial-gradient(circle at 15% 20%, rgba(194, 155, 114, 0.04) 0%, transparent 40%),
    radial-gradient(circle at 85% 60%, rgba(230, 57, 70, 0.04) 0%, transparent 40%),
    radial-gradient(circle at 50% 90%, rgba(0, 245, 212, 0.04) 0%, transparent 40%);
  transition: background var(--transition-normal);
}

/* Light Theme Atmosphere */
[data-theme="light"] .bg-atmosphere {
  background: 
    radial-gradient(circle at 15% 20%, rgba(139, 90, 43, 0.04) 0%, transparent 40%),
    radial-gradient(circle at 85% 60%, rgba(207, 34, 46, 0.04) 0%, transparent 40%),
    radial-gradient(circle at 50% 90%, rgba(9, 105, 218, 0.04) 0%, transparent 40%);
}

/* Eye-care Theme Atmosphere (Warm Amber Parchment Glow) */
[data-theme="eyecare"] .bg-atmosphere {
  background: 
    radial-gradient(circle at 20% 20%, rgba(160, 115, 65, 0.06) 0%, transparent 50%),
    radial-gradient(circle at 80% 80%, rgba(184, 134, 11, 0.05) 0%, transparent 50%);
}

/* Dynamic Era Filter on Body */
body.theme-ww1 .bg-atmosphere {
  background: radial-gradient(circle at 50% 30%, rgba(194, 155, 114, 0.08) 0%, transparent 60%),
              radial-gradient(circle at 20% 80%, rgba(139, 115, 85, 0.06) 0%, transparent 50%);
}

body.theme-ww2 .bg-atmosphere {
  background: radial-gradient(circle at 50% 30%, rgba(230, 57, 70, 0.08) 0%, transparent 60%),
              radial-gradient(circle at 80% 80%, rgba(69, 123, 157, 0.06) 0%, transparent 50%);
}

body.theme-coldwar .bg-atmosphere {
  background: radial-gradient(circle at 50% 30%, rgba(0, 245, 212, 0.08) 0%, transparent 60%),
              radial-gradient(circle at 20% 80%, rgba(255, 0, 85, 0.06) 0%, transparent 50%);
}

/* Layout Containers */
.container {
  width: 100%;
  max-width: var(--container-max-width);
  margin: 0 auto;
  padding: 0 24px;
}

/* Typography Classes */
h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-heading);
  color: var(--text-bright);
  line-height: 1.3;
}

.heading-serif {
  font-family: var(--font-serif);
}

.heading-tech {
  font-family: var(--font-tech);
}

p {
  margin-bottom: 1rem;
}

p:last-child {
  margin-bottom: 0;
}

/* Custom Scrollbar */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

::-webkit-scrollbar-track {
  background: var(--bg-primary);
}

::-webkit-scrollbar-thumb {
  background: rgba(140, 140, 140, 0.25);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: rgba(140, 140, 140, 0.45);
}

/* Section Wrapper */
.chapter-section {
  padding: 80px 0;
  border-bottom: 1px solid var(--border-color);
  position: relative;
}

.chapter-header {
  text-align: center;
  margin-bottom: 50px;
}

.chapter-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 16px;
  border-radius: 30px;
  font-family: var(--font-tech);
  font-size: 0.9rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin-bottom: 16px;
}

.chapter-title {
  font-size: 2.4rem;
  margin-bottom: 12px;
}

.chapter-period {
  font-family: var(--font-tech);
  font-size: 1.2rem;
  opacity: 0.85;
  margin-bottom: 16px;
}

.chapter-intro {
  max-width: 860px;
  margin: 0 auto;
  font-size: 1.15rem;
  color: var(--text-main);
  line-height: 1.8;
  background: var(--bg-card);
  padding: 20px 28px;
  border-radius: var(--radius-md);
  border-left: 4px solid;
  border: 1px solid var(--border-color);
  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.04);
}