/* ============================================================
   Mathagram.org — Global Stylesheet
   Light theme foundation, design tokens, and shared components
   ============================================================ */

/* ----- Font Imports ----- */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700;800&family=JetBrains+Mono:wght@400;500;600&display=swap');

/* ============================================================
   Design Tokens (CSS Custom Properties)
   ============================================================ */
:root {
  /* Brand colors */
  --color-primary:       #00e5c8;
  --color-primary-light: #5effe0;
  --color-primary-dark:  #00b89f;

  /* Category colors */
  --color-math:          #3b82f6;
  --color-math-bg:       #eff6ff;
  --color-science:       #22c55e;
  --color-science-bg:    #f0fdf4;
  --color-data:          #ef4444;
  --color-data-bg:       #fef2f2;
  --color-logic:         #f97316;
  --color-logic-bg:      #fff7ed;

  /* XP / Level */
  --color-xp:            #eab308;

  /* Light theme palette */
  --color-bg:            #f8f9fa;
  --color-white:         #ffffff;
  --color-text:          #1a1a2e;
  --color-text-secondary:#64748b;
  --color-text-muted:    #94a3b8;
  --color-border:        #e2e8f0;

  /* Shadows */
  --shadow-sm:  0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md:  0 4px 6px -1px rgba(0, 0, 0, 0.08), 0 2px 4px -2px rgba(0, 0, 0, 0.05);
  --shadow-lg:  0 10px 15px -3px rgba(0, 0, 0, 0.08), 0 4px 6px -4px rgba(0, 0, 0, 0.05);

  /* Border radii */
  --radius:    12px;
  --radius-lg: 16px;

  /* Typography */
  --font-sans: 'Inter', system-ui, -apple-system, sans-serif;
  --font-mono: 'JetBrains Mono', ui-monospace, monospace;
}

/* ============================================================
   Reset
   ============================================================ */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-sans);
  color: var(--color-text);
  background-color: var(--color-bg);
  line-height: 1.6;
  min-height: 100vh;
}

img {
  max-width: 100%;
  display: block;
}

a {
  color: inherit;
  text-decoration: none;
}

ul, ol {
  list-style: none;
}

/* ============================================================
   Container
   ============================================================ */
.container {
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 24px;
}

/* ============================================================
   Navigation — fixed top bar
   ============================================================ */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  height: 64px;
  display: flex;
  align-items: center;
  background: rgba(255, 255, 255, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border);
}

.nav .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav-logo {
  font-size: 1.25rem;
  font-weight: 800;
  color: var(--color-text);
  display: flex;
  align-items: center;
  gap: 8px;
}

.nav-logo span {
  color: var(--color-primary-dark);
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 32px;
}

.nav-links a {
  font-size: 0.925rem;
  font-weight: 500;
  color: var(--color-text-secondary);
  transition: color 0.2s;
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--color-text);
}

/* Push page content below fixed nav */
body {
  padding-top: 64px;
}

/* ============================================================
   Buttons
   ============================================================ */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 10px 24px;
  font-family: var(--font-sans);
  font-size: 0.925rem;
  font-weight: 600;
  border: 2px solid transparent;
  border-radius: var(--radius);
  cursor: pointer;
  transition: background 0.2s, color 0.2s, box-shadow 0.2s, transform 0.15s;
}

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

.btn:active {
  transform: translateY(0);
}

.btn-primary {
  background: var(--color-primary);
  color: var(--color-text);
  border-color: var(--color-primary);
}

.btn-primary:hover {
  background: var(--color-primary-light);
  border-color: var(--color-primary-light);
  box-shadow: var(--shadow-md);
}

.btn-outline {
  background: transparent;
  color: var(--color-text);
  border-color: var(--color-border);
}

.btn-outline:hover {
  border-color: var(--color-primary);
  color: var(--color-primary-dark);
  box-shadow: var(--shadow-sm);
}

/* ============================================================
   Category Sections
   ============================================================ */
.category-section {
  padding: 48px 0;
  border-radius: var(--radius-lg);
  margin-bottom: 32px;
}

.category-section .category-title {
  font-size: 1.5rem;
  font-weight: 700;
  margin-bottom: 24px;
}

/* Math — blue */
.category-math {
  background: var(--color-math-bg);
}
.category-math .category-title {
  color: var(--color-math);
}

/* Science — green */
.category-science {
  background: var(--color-science-bg);
}
.category-science .category-title {
  color: var(--color-science);
}

/* Data Analysis — red */
.category-data {
  background: var(--color-data-bg);
}
.category-data .category-title {
  color: var(--color-data);
}

/* Logic — orange */
.category-logic {
  background: var(--color-logic-bg);
}
.category-logic .category-title {
  color: var(--color-logic);
}

/* ============================================================
   Course Cards & Grid
   ============================================================ */
.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 24px;
}

.course-card {
  background: var(--color-white);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 24px;
  transition: transform 0.2s, box-shadow 0.2s;
}

.course-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

/* ============================================================
   Footer
   ============================================================ */
.footer {
  margin-top: 64px;
  padding: 48px 0 32px;
  text-align: center;
  border-top: 1px solid var(--color-border);
}

.footer-logo {
  font-size: 1.125rem;
  font-weight: 700;
  margin-bottom: 16px;
}

.footer-logo span {
  color: var(--color-primary-dark);
}

.footer-links {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 24px;
  margin-bottom: 24px;
}

.footer-links a {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  transition: color 0.2s;
}

.footer-links a:hover {
  color: var(--color-text);
}

.footer-copy {
  font-size: 0.8rem;
  color: var(--color-text-muted);
}

/* ============================================================
   Responsive — Mobile (max-width: 768px)
   ============================================================ */
@media (max-width: 768px) {
  /* Hide nav links on mobile */
  .nav-links {
    display: none;
  }

  .container {
    padding: 0 16px;
  }

  .course-grid {
    grid-template-columns: 1fr;
    gap: 16px;
  }

  .category-section {
    padding: 32px 0;
    margin-bottom: 24px;
  }

  .category-section .category-title {
    font-size: 1.25rem;
  }

  .footer {
    margin-top: 48px;
    padding: 32px 0 24px;
  }
}