@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&family=Poppins:wght@400;500;600;700;800&display=swap');

/* =============================================
   STUDY HUB — PREMIUM DESIGN SYSTEM
   ============================================= */

:root {
  /* Dark Theme (Default) — Rich Slate palette */
  --bg-primary: #0f172a;
  --bg-secondary: #111827;
  --surface: rgba(30, 41, 59, 0.65);
  --surface-solid: #1e293b;
  --surface-hover: #243041;
  --sidebar-bg: #0e1525;
  --sidebar-hover: rgba(255, 255, 255, 0.05);
  --sidebar-active: rgba(139, 92, 246, 0.1);

  --accent-primary: #8b5cf6;   /* Violet */
  --accent-secondary: #06b6d4; /* Cyan */
  --accent-highlight: #38bdf8; /* Sky */
  --brand-gradient: linear-gradient(135deg, var(--accent-primary), var(--accent-secondary));
  --success: #10b981;
  --warning: #f59e0b;
  --danger: #ef4444;

  --text-primary: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;

  --border: rgba(255, 255, 255, 0.08);
  --border-hover: rgba(255, 255, 255, 0.15);
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 20px;

  --shadow-sm: 0 1px 2px rgba(0,0,0,0.15);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.25);
  --shadow-lg: 0 20px 50px rgba(0,0,0,0.45);
  --shadow-glow: 0 0 20px rgba(139, 92, 246, 0.15);

  --transition-speed: 0.2s;
  --transition-smooth: 0.35s cubic-bezier(0.4, 0, 0.2, 1);
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-display: 'Poppins', var(--font-sans);
  --font-mono: ui-monospace, 'Cascadia Code', 'SF Mono', Menlo, Monaco, monospace;
}

[data-theme="light"] {
  --bg-primary: #f8fafc;
  --bg-secondary: #ffffff;
  --surface: rgba(241, 245, 249, 0.8);
  --surface-solid: #f1f5f9;
  --surface-hover: #e2e8f0;
  --sidebar-bg: #f1f5f9;
  --sidebar-hover: rgba(0, 0, 0, 0.04);
  --sidebar-active: rgba(139, 92, 246, 0.08);

  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #94a3b8;

  --border: rgba(0, 0, 0, 0.08);
  --border-hover: rgba(0, 0, 0, 0.15);

  --shadow-sm: 0 1px 2px rgba(0,0,0,0.05);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.08);
  --shadow-lg: 0 20px 50px rgba(0,0,0,0.12);
  --shadow-glow: 0 0 20px rgba(139, 92, 246, 0.08);
}

/* ===== RESET & BASE ===== */
* { box-sizing: border-box; margin: 0; padding: 0; }

body {
    font-family: var(--font-sans);
    background: var(--bg-primary);
    color: var(--text-primary);
    display: flex; height: 100vh; overflow: hidden;
    transition: background var(--transition-speed), color var(--transition-speed);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* Custom Scrollbar */
::-webkit-scrollbar { width: 5px; height: 5px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: rgba(148, 163, 184, 0.2); border-radius: 10px; }
::-webkit-scrollbar-thumb:hover { background: rgba(148, 163, 184, 0.35); }

/* Focus Visible — Accessibility */
*:focus-visible {
    outline: 2px solid var(--accent-primary);
    outline-offset: 2px;
    border-radius: var(--radius-sm);
}

/* =============================================
   SIDEBAR
   ============================================= */
.sidebar {
    width: 320px; min-width: 320px; height: 100vh;
    background: var(--sidebar-bg);
    border-right: 1px solid var(--border);
    display: flex; flex-direction: column;
    transition: transform var(--transition-smooth), background var(--transition-speed);
    z-index: 100; overflow: hidden;
}

/* --- Sidebar Header --- */
.sidebar-header {
    padding: 1.25rem 1.5rem 1rem; border-bottom: 1px solid var(--border);
    display: flex; align-items: center; justify-content: space-between; flex-shrink: 0;
}

.logo { display: flex; align-items: center; gap: 0.75rem; }
.logo-icon {
    width: 34px; height: 34px; border-radius: var(--radius-md);
    display: flex; align-items: center; justify-content: center;
    background: var(--brand-gradient); color: #fff;
    font-family: var(--font-display); font-weight: 800; font-size: 0.9rem;
    box-shadow: var(--shadow-sm), var(--shadow-glow);
}
.logo-text {
    font-family: var(--font-display); font-size: 1.1rem; font-weight: 700;
    letter-spacing: -0.02em; color: var(--text-primary);
}

/* --- Theme Toggle --- */
.theme-toggle {
    width: 44px; height: 24px; border-radius: 12px; border: 1px solid var(--border);
    cursor: pointer; position: relative; background: var(--surface);
    transition: all var(--transition-speed);
}
.theme-toggle:hover { border-color: var(--border-hover); background: var(--surface-hover); }
.theme-toggle::after {
    content: ''; position: absolute; top: 2px; left: 2px; width: 18px; height: 18px;
    border-radius: 50%; background: var(--accent-primary);
    transition: transform 0.3s cubic-bezier(0.4,0,0.2,1);
    box-shadow: 0 0 8px rgba(139, 92, 246, 0.3);
}
[data-theme="light"] .theme-toggle::after { transform: translateX(20px); background: var(--warning); box-shadow: 0 0 8px rgba(245, 158, 11, 0.3); }
.theme-toggle .icon { position: absolute; top: 50%; transform: translateY(-50%); font-size: 11px; z-index: 1; }
.theme-toggle .sun { left: 5px; opacity: 0.8; }
.theme-toggle .moon { right: 5px; opacity: 0.8; }

/* --- Search Box (Glassmorphism) --- */
.search-box {
    padding: 0.75rem 1.25rem; flex-shrink: 0;
    position: relative;
}
.search-box input {
    width: 100%; padding: 0.6rem 2.5rem 0.6rem 2.2rem; border-radius: var(--radius-md);
    border: 1px solid var(--border); background: var(--surface);
    color: var(--text-primary); font-family: var(--font-sans); font-size: 0.875rem;
    outline: none; transition: all var(--transition-speed);
    backdrop-filter: blur(12px); -webkit-backdrop-filter: blur(12px);
}
.search-box input::placeholder { color: var(--text-muted); }
.search-box input:focus {
    border-color: var(--accent-primary);
    box-shadow: 0 0 0 3px rgba(139, 92, 246, 0.15);
    background: var(--surface-hover);
}
.search-box::before {
    content: '🔍'; position: absolute; left: 2rem; top: 50%; transform: translateY(-50%);
    font-size: 0.8rem; z-index: 1; opacity: 0.5;
}
.search-shortcut {
    position: absolute; right: 2rem; top: 50%; transform: translateY(-50%);
    font-size: 0.65rem; color: var(--text-muted); background: var(--bg-primary);
    padding: 0.15rem 0.45rem; border-radius: var(--radius-sm); border: 1px solid var(--border);
    pointer-events: none; font-family: var(--font-sans); font-weight: 500;
}

/* --- Progress Dashboard --- */
.dashboard-stats {
    padding: 0.85rem 1.25rem; border-bottom: 1px solid var(--border);
    background: rgba(139, 92, 246, 0.03);
}
.progress-container { }
.progress-info {
    display: flex; justify-content: space-between; align-items: center;
    font-size: 0.75rem; margin-bottom: 0.5rem; font-weight: 500; color: var(--text-muted);
    letter-spacing: 0.02em;
}
.progress-bar-bg {
    height: 4px; background: var(--border); border-radius: 2px; overflow: hidden;
}
.progress-bar-fill {
    height: 100%; width: 0%;
    background: var(--brand-gradient);
    border-radius: 2px; transition: width 0.8s cubic-bezier(0.4,0,0.2,1);
}

/* --- Navigation --- */
.nav-content { flex: 1; overflow-y: auto; padding: 0.5rem 0; }

.category { margin-bottom: 1px; }
.category-btn {
    width: 100%; padding: 0.7rem 1.25rem; display: flex; align-items: center; gap: 0.65rem;
    background: var(--sidebar-bg); border: none; color: var(--text-primary);
    font-family: var(--font-display); font-size: 0.85rem; font-weight: 600;
    cursor: pointer; transition: background var(--transition-speed); text-align: left;
    position: sticky; top: 0; z-index: 10;
    border-bottom: 1px solid var(--border);
    letter-spacing: -0.01em;
}
.category-btn:hover { background: var(--sidebar-hover); }
.category-btn .cat-icon { font-size: 1rem; opacity: 0.85; flex-shrink: 0; }
.category-btn .count {
    margin-left: auto; background: var(--surface); padding: 0.15rem 0.5rem;
    border-radius: 10px; font-size: 0.7rem; color: var(--text-muted);
    border: 1px solid var(--border); font-family: var(--font-sans); font-weight: 500;
}
.category-btn .arrow {
    transition: transform 0.25s cubic-bezier(0.4,0,0.2,1);
    font-size: 0.55rem; color: var(--text-muted); flex-shrink: 0;
}
.category-btn.open .arrow { transform: rotate(90deg); }

/* --- Topic List --- */
.topic-list { display: none; padding: 0.2rem 0; }
.topic-list.open { display: block; animation: slideDown 0.25s cubic-bezier(0.4,0,0.2,1); }

@keyframes slideDown {
    from { opacity: 0; transform: translateY(-4px); }
    to { opacity: 1; transform: translateY(0); }
}

.topic-link {
    display: flex; align-items: center; gap: 0.5rem;
    padding: 0.4rem 1.25rem 0.4rem 2.5rem;
    color: var(--text-secondary); text-decoration: none; font-size: 0.82rem;
    transition: all var(--transition-speed);
    border-left: 2px solid transparent; cursor: pointer; line-height: 1.5;
    position: relative;
}
.topic-link:hover {
    background: var(--sidebar-hover); color: var(--text-primary);
}
.topic-link.active {
    background: var(--sidebar-active); color: var(--accent-primary); font-weight: 500;
    border-left-color: var(--accent-primary);
}
.topic-link::before {
    content: ''; width: 4px; height: 4px; border-radius: 50%;
    background: var(--text-muted); flex-shrink: 0; transition: all 0.2s; opacity: 0.4;
}
.topic-link:hover::before {
    background: var(--accent-secondary); opacity: 0.8;
}
.topic-link.active::before {
    background: var(--accent-primary); box-shadow: 0 0 8px var(--accent-primary); opacity: 1;
}
.topic-link.visited::after {
    content: '✓'; margin-left: auto; color: var(--success); font-weight: 700; font-size: 0.75rem;
}

.hidden { display: none !important; }

/* --- Sidebar Footer --- */
.sidebar-footer {
    padding: 0.85rem 1.25rem; border-top: 1px solid var(--border); flex-shrink: 0;
    font-size: 0.7rem; color: var(--text-muted); text-align: center;
    letter-spacing: 0.02em;
}

.btn-reset {
    margin-top: 0.6rem; background: transparent; color: var(--text-muted);
    border: 1px solid var(--border); padding: 0.35rem 0.75rem;
    border-radius: var(--radius-sm); font-size: 0.68rem; cursor: pointer;
    transition: all 0.2s; font-family: var(--font-sans); font-weight: 500; width: 100%;
}
.btn-reset:hover { background: rgba(239, 68, 68, 0.08); color: var(--danger); border-color: rgba(239, 68, 68, 0.25); }

/* =============================================
   MAIN CONTENT AREA
   ============================================= */
.main { flex: 1; display: flex; flex-direction: column; overflow: hidden; background: var(--bg-primary); }

/* --- Topbar (Glassmorphism) --- */
.topbar {
    padding: 0.65rem 2rem; border-bottom: 1px solid var(--border);
    display: flex; align-items: center; gap: 1.25rem; flex-shrink: 0;
    background: var(--surface); backdrop-filter: blur(20px); -webkit-backdrop-filter: blur(20px);
    z-index: 50; transition: background var(--transition-speed);
    position: relative;
}

.hamburger {
    display: none; background: none; border: none; color: var(--text-primary);
    font-size: 1.3rem; cursor: pointer; padding: 0.25rem;
}

.breadcrumb {
    font-size: 0.82rem; color: var(--text-muted); display: flex; align-items: center; gap: 0.5rem;
    font-weight: 400;
}
.breadcrumb span { color: var(--text-primary); font-weight: 500; }
.breadcrumb::before {
    content: ''; display: inline-block; width: 3px; height: 14px;
    background: var(--accent-primary); border-radius: 2px; flex-shrink: 0;
}

/* --- Reading Progress Bar --- */
.reading-progress {
    position: absolute; bottom: 0; left: 0; width: 100%; height: 2px;
    background: transparent; overflow: hidden;
}
.reading-progress-fill {
    height: 100%; width: 0%;
    background: var(--brand-gradient);
    border-radius: 0 2px 2px 0;
    transition: width 0.15s ease-out;
}

/* --- Top Timers --- */
.top-timers { margin-left: auto; display: flex; align-items: center; gap: 1.25rem; }
.timer-item { display: flex; flex-direction: column; align-items: flex-end; }
.timer-val {
    font-family: var(--font-mono); font-size: 0.9rem; font-weight: 600;
    color: var(--text-primary); line-height: 1.2;
    letter-spacing: 0.02em;
}
.timer-lbl {
    font-size: 0.6rem; color: var(--text-muted); text-transform: uppercase;
    letter-spacing: 0.06em; font-weight: 500;
}

.stopwatch {
    background: var(--bg-secondary); border: 1px solid var(--border);
    padding: 0.3rem 0.6rem; border-radius: var(--radius-md);
    display: flex; align-items: center; gap: 0.7rem;
    box-shadow: var(--shadow-sm);
}
.sw-btns { display: flex; gap: 0.3rem; }
.sw-btn {
    background: none; border: none; cursor: pointer; padding: 2px;
    border-radius: var(--radius-sm); color: var(--text-muted);
    transition: all 0.2s; font-size: 0.85rem;
    display: flex; align-items: center; justify-content: center;
    width: 24px; height: 24px;
}
.sw-btn:hover { background: var(--sidebar-hover); color: var(--text-primary); }
.sw-btn.active { color: var(--danger); }

/* --- Content Frame --- */
.content-frame {
    flex: 1; background: var(--bg-primary);
    transition: background var(--transition-speed); overflow: hidden;
    position: relative;
}
.content-frame iframe {
    width: 100%; height: 100%; border: none; background: transparent;
    opacity: 0; transition: opacity 0.3s ease;
}
.content-frame iframe.loaded { opacity: 1; }

/* --- Welcome Screen --- */
.welcome {
    display: flex; flex-direction: column; align-items: center; justify-content: center;
    height: 100%; text-align: center; padding: 2rem;
    background: var(--bg-primary);
    background-image:
        radial-gradient(ellipse at 30% 20%, rgba(139, 92, 246, 0.06) 0%, transparent 50%),
        radial-gradient(ellipse at 70% 80%, rgba(6, 182, 212, 0.05) 0%, transparent 50%);
}
.welcome-icon {
    font-size: 3rem; margin-bottom: 1.5rem;
    background: var(--surface); width: 80px; height: 80px;
    display: flex; align-items: center; justify-content: center;
    border-radius: 24px; border: 1px solid var(--border);
    box-shadow: var(--shadow-md), var(--shadow-glow);
    animation: welcomePulse 3s ease-in-out infinite;
}
@keyframes welcomePulse {
    0%, 100% { box-shadow: var(--shadow-md), 0 0 20px rgba(139, 92, 246, 0.1); }
    50% { box-shadow: var(--shadow-md), 0 0 35px rgba(139, 92, 246, 0.2); }
}
.welcome h2 {
    font-family: var(--font-display); font-size: 2.5rem; font-weight: 800;
    margin-bottom: 0.75rem; letter-spacing: -0.03em;
    background: linear-gradient(135deg, var(--text-primary), var(--accent-primary), var(--accent-secondary));
    background-size: 200% 200%;
    -webkit-background-clip: text; background-clip: text; -webkit-text-fill-color: transparent;
    animation: gradientShift 6s ease-in-out infinite;
}
@keyframes gradientShift {
    0%, 100% { background-position: 0% 50%; }
    50% { background-position: 100% 50%; }
}
.welcome p {
    color: var(--text-muted); font-size: 1.05rem; max-width: 480px; line-height: 1.7;
    margin-bottom: 1.5rem;
}
.welcome-hint {
    display: inline-flex; align-items: center; gap: 0.5rem;
    color: var(--text-muted); font-size: 0.8rem;
    background: var(--surface); padding: 0.4rem 1rem; border-radius: 20px;
    border: 1px solid var(--border);
}
.welcome-hint kbd {
    background: var(--bg-primary); padding: 0.15rem 0.4rem; border-radius: var(--radius-sm);
    border: 1px solid var(--border); font-family: var(--font-sans); font-size: 0.7rem; font-weight: 600;
}

/* --- Overlay --- */
.sidebar-overlay {
    display: none; position: fixed; inset: 0;
    background: rgba(0,0,0,0.6); backdrop-filter: blur(4px); -webkit-backdrop-filter: blur(4px);
    z-index: 99;
}

/* =============================================
   RESPONSIVE
   ============================================= */
@media (max-width: 900px) {
    .sidebar {
        position: fixed; left: 0; top: 0; transform: translateX(-100%);
        box-shadow: var(--shadow-lg);
    }
    .sidebar.open { transform: translateX(0); }
    .sidebar-overlay.open { display: block; }
    .hamburger { display: block; }
    .topbar { padding: 0.65rem 1.25rem; }
}

@media (max-width: 480px) {
    .sidebar { width: 100%; min-width: 100%; }
    .welcome h2 { font-size: 1.8rem; }
    .top-timers { flex-wrap: wrap; gap: 0.5rem; justify-content: flex-end; }
    .search-shortcut { display: none; }
    .welcome-hint { display: none; }
}