/**
 * main.css - Core design tokens, theme variables, typography, and base layout
 */

:root {
  /* Color Palette - Light Mode */
  --bg-primary: #f8fafc;
  --bg-surface: #ffffff;
  --bg-surface-subtle: #f1f5f9;
  --bg-surface-elevated: #ffffff;
  
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #94a3b8;
  --text-inverse: #ffffff;

  --border-subtle: #e2e8f0;
  --border-strong: #cbd5e1;

  /* Accent Colors */
  --primary: #2563eb;
  --primary-hover: #1d4ed8;
  --primary-light: #eff6ff;
  --primary-text: #1e40af;

  --success: #10b981;
  --success-light: #ecfdf5;
  --success-text: #065f46;

  --warning: #f59e0b;
  --warning-light: #fffbeb;
  --warning-text: #92400e;

  --danger: #ef4444;
  --danger-light: #fef2f2;
  --danger-text: #991b1b;

  --subject-math: #2563eb;
  --subject-swe: #059669;
  --subject-eng: #7c3aed;

  /* Typography */
  --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;

  /* Shadows */
  --shadow-sm: 0 1px 2px 0 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, 0.03);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 8px 10px -6px rgba(0, 0, 0, 0.05);

  /* Border Radius */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-full: 9999px;

  /* Layout */
  --max-width: 1200px;
  --header-height: 64px;
}

[data-theme="dark"] {
  --bg-primary: #0f172a;
  --bg-surface: #1e293b;
  --bg-surface-subtle: #334155;
  --bg-surface-elevated: #1e293b;

  --text-primary: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-muted: #64748b;
  --text-inverse: #0f172a;

  --border-subtle: #334155;
  --border-strong: #475569;

  --primary: #3b82f6;
  --primary-hover: #60a5fa;
  --primary-light: #1e3a8a;
  --primary-text: #93c5fd;

  --success: #10b981;
  --success-light: #064e3b;
  --success-text: #6ee7b7;

  --warning: #f59e0b;
  --warning-light: #78350f;
  --warning-text: #fcd34d;

  --danger: #f87171;
  --danger-light: #7f1d1d;
  --danger-text: #fca5a5;

  --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, 0.4);
}

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

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

body {
  font-family: var(--font-family);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.5;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  -webkit-font-smoothing: antialiased;
}

/* App Header */
.app-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--header-height);
  background-color: var(--bg-surface);
  border-bottom: 1px solid var(--border-subtle);
  display: flex;
  align-items: center;
  box-shadow: var(--shadow-sm);
}

.header-inner {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.25rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.brand-logo {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  text-decoration: none;
  color: var(--text-primary);
  font-weight: 700;
  font-size: 1.2rem;
  cursor: pointer;
}

.logo-badge {
  background: linear-gradient(135deg, #2563eb, #3b82f6);
  color: #fff;
  font-size: 0.8rem;
  font-weight: 800;
  padding: 0.25rem 0.5rem;
  border-radius: var(--radius-sm);
  letter-spacing: 0.5px;
}

.brand-text {
  font-weight: 800;
  letter-spacing: -0.5px;
}

.brand-grade {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-secondary);
  background-color: var(--bg-surface-subtle);
  padding: 0.15rem 0.4rem;
  border-radius: var(--radius-sm);
}

.main-nav {
  display: flex;
  align-items: center;
  gap: 1.25rem;
}

.nav-link {
  text-decoration: none;
  color: var(--text-secondary);
  font-weight: 500;
  font-size: 0.95rem;
  padding: 0.4rem 0.6rem;
  border-radius: var(--radius-sm);
  transition: all 0.15s ease;
}

.nav-link:hover {
  color: var(--primary);
  background-color: var(--bg-surface-subtle);
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

/* Main Content Area */
.app-main {
  flex: 1;
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 1.5rem 1.25rem 3rem;
}

/* App Footer */
.app-footer {
  background-color: var(--bg-surface);
  border-top: 1px solid var(--border-subtle);
  padding: 1.5rem 0;
  font-size: 0.85rem;
  color: var(--text-secondary);
  text-align: center;
}

.footer-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.25rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.4rem;
}

/* Utilities & Animations */
.hidden {
  display: none !important;
}

.animate-fade-in {
  animation: fadeIn 0.25s ease-out forwards;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(6px); }
  to { opacity: 1; transform: translateY(0); }
}

.math-expr {
  font-family: var(--font-mono);
  background-color: var(--bg-surface-subtle);
  padding: 0.15rem 0.35rem;
  border-radius: 4px;
  font-size: 0.95em;
}