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

:root {
    --primary: #3b82f6;
    --primary-dark: #2563eb;
    --secondary: #f43f5e;
    --accent: #06b6d4;
    --accent2: #8b5cf6;
    --bg: #f0f4f8;
    --bg2: #e2e8f0;
    --card: #ffffff;
    --card-border: rgba(0,0,0,0.06);
    --text: #1e293b;
    --text2: #475569;
    --muted: #94a3b8;
    --ok: #10b981;
    --bad: #ef4444;
    --glass: rgba(255,255,255,0.7);
    --glass-border: rgba(255,255,255,0.3);
    --shadow: 0 4px 24px rgba(0,0,0,0.08);
    --shadow-lg: 0 8px 40px rgba(0,0,0,0.12);
    --radius: 14px;
    --transition: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

[data-theme="dark"] {
    --bg: #0f172a;
    --bg2: #1e293b;
    --card: #1e293b;
    --card-border: rgba(255,255,255,0.08);
    --text: #f1f5f9;
    --text2: #94a3b8;
    --muted: #64748b;
    --glass: rgba(30,41,59,0.8);
    --glass-border: rgba(255,255,255,0.1);
    --shadow: 0 4px 24px rgba(0,0,0,0.3);
    --shadow-lg: 0 8px 40px rgba(0,0,0,0.4);
}

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

body {
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.6;
    transition: background var(--transition), color var(--transition);
    overflow-x: hidden;
}

/* ── Header ── */
header {
    background: linear-gradient(135deg, #1e3a5f 0%, #0f766e 50%, #1e40af 100%);
    color: white;
    padding: 2.5rem 1.5rem 2rem;
    text-align: center;
    position: relative;
    overflow: hidden;
}

header::before {
    content: '';
    position: absolute;
    inset: 0;
    background: radial-gradient(circle at 20% 50%, rgba(6,182,212,0.3) 0%, transparent 50%),
                radial-gradient(circle at 80% 50%, rgba(139,92,246,0.2) 0%, transparent 50%);
    pointer-events: none;
}

header h1 {
    font-size: clamp(1.4rem, 4vw, 2rem);
    font-weight: 800;
    letter-spacing: -0.02em;
    position: relative;
}

header p {
    opacity: 0.85;
    margin-top: 0.4rem;
    font-size: 0.95rem;
    font-weight: 400;
    position: relative;
}

.header-controls {
    position: absolute;
    top: 1rem;
    right: 1.2rem;
    display: flex;
    gap: 0.5rem;
    z-index: 10;
}

.theme-toggle {
    background: rgba(255,255,255,0.15);
    border: 1px solid rgba(255,255,255,0.25);
    color: white;
    width: 40px;
    height: 40px;
    border-radius: 50%;
    cursor: pointer;
    font-size: 1.15rem;
    display: grid;
    place-items: center;
    transition: var(--transition);
    backdrop-filter: blur(8px);
}

.theme-toggle:hover { background: rgba(255,255,255,0.25); transform: rotate(20deg); }

/* ── Wrapper ── */
.wrapper {
    max-width: 1300px;
    margin: 0 auto;
    padding: 1.5rem 1.2rem 3rem;
}

/* ── Tabs Navigation ── */
.tab-nav {
    display: flex;
    gap: 0.4rem;
    margin-bottom: 1.5rem;
    background: var(--card);
    border-radius: var(--radius);
    padding: 0.35rem;
    box-shadow: var(--shadow);
    border: 1px solid var(--card-border);
    overflow-x: auto;
    scrollbar-width: none;
}

.tab-nav::-webkit-scrollbar { display: none; }

.tab-btn {
    flex: 1;
    min-width: max-content;
    padding: 0.7rem 1rem;
    border: none;
    border-radius: 10px;
    background: transparent;
    color: var(--text2);
    font-weight: 600;
    font-size: 0.88rem;
    cursor: pointer;
    transition: var(--transition);
    white-space: nowrap;
    font-family: inherit;
}

.tab-btn:hover { background: var(--bg); }

.tab-btn.active {
    background: var(--primary);
    color: white;
    box-shadow: 0 2px 10px rgba(59,130,246,0.3);
}

.tab-panel { display: none; animation: fadeSlide 0.4s ease; }
.tab-panel.active { display: block; }

@keyframes fadeSlide {
    from { opacity: 0; transform: translateY(12px); }
    to { opacity: 1; transform: translateY(0); }
}

/* ── Stats ── */
.stats {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 0.8rem;
    margin-bottom: 1.5rem;
}

.stat-card {
    background: var(--card);
    border-radius: var(--radius);
    padding: 1rem 1.2rem;
    box-shadow: var(--shadow);
    border: 1px solid var(--card-border);
    position: relative;
    overflow: hidden;
    transition: transform var(--transition), box-shadow var(--transition);
}

.stat-card:hover { transform: translateY(-2px); box-shadow: var(--shadow-lg); }

.stat-card::before {
    content: '';
    position: absolute;
    top: 0; left: 0; right: 0;
    height: 3px;
}

.stat-card:nth-child(1)::before { background: linear-gradient(90deg, var(--primary), var(--accent)); }
.stat-card:nth-child(2)::before { background: linear-gradient(90deg, var(--accent2), var(--secondary)); }
.stat-card:nth-child(3)::before { background: linear-gradient(90deg, var(--ok), var(--accent)); }
.stat-card:nth-child(4)::before { background: linear-gradient(90deg, var(--secondary), var(--accent2)); }

.stat-card .label {
    font-size: 0.78rem;
    color: var(--muted);
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.04em;
    margin-bottom: 0.3rem;
}

.stat-card .value {
    font-size: 1.5rem;
    font-weight: 800;
    background: linear-gradient(135deg, var(--primary), var(--accent));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.stat-card .icon {
    position: absolute;
    top: 0.8rem;
    right: 0.8rem;
    font-size: 1.3rem;
    opacity: 0.4;
}

/* ── Cards ── */
.card {
    background: var(--card);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    border: 1px solid var(--card-border);
    overflow: hidden;
    transition: transform var(--transition), box-shadow var(--transition);
}

.card:hover { box-shadow: var(--shadow-lg); }

.card-head {
    padding: 1rem 1.2rem;
    border-bottom: 1px solid var(--card-border);
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 0.8rem;
    flex-wrap: wrap;
}

.card-head h2 {
    font-size: 1.05rem;
    font-weight: 700;
    color: var(--text);
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.card-body { padding: 1.2rem; }

/* ── Layout ── */
.layout {
    display: grid;
    grid-template-columns: 1.3fr 1fr;
    gap: 1rem;
}

/* ── Topic List ── */
.topic-list {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 0.5rem;
    margin-bottom: 1rem;
}

.topic-btn {
    border: 1px solid var(--card-border);
    background: var(--bg);
    border-radius: 10px;
    padding: 0.65rem 0.8rem;
    text-align: left;
    cursor: pointer;
    color: var(--text);
    transition: var(--transition);
    font-size: 0.85rem;
    font-weight: 500;
    font-family: inherit;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.topic-btn .check-icon {
    width: 18px;
    height: 18px;
    border-radius: 50%;
    border: 2px solid var(--muted);
    display: inline-flex;
    align-items: center;
    justify-content: center;
    font-size: 0.65rem;
    flex-shrink: 0;
    transition: var(--transition);
}

.topic-btn.mastered .check-icon {
    background: var(--ok);
    border-color: var(--ok);
    color: white;
}

.topic-btn:hover { border-color: var(--primary); transform: translateX(3px); }

.topic-btn.active {
    background: linear-gradient(135deg, var(--primary), var(--primary-dark));
    color: white;
    border-color: transparent;
    box-shadow: 0 2px 12px rgba(59,130,246,0.25);
}

.topic-btn.active .check-icon { border-color: rgba(255,255,255,0.5); }

.topic-box {
    background: var(--bg);
    border: 1px solid var(--card-border);
    border-radius: var(--radius);
    padding: 1.2rem;
    animation: fadeSlide 0.3s ease;
}

.topic-box h3 {
    color: var(--primary);
    margin-bottom: 0.5rem;
    font-size: 1.05rem;
    font-weight: 700;
}

.topic-box .trigger {
    color: var(--accent);
    font-weight: 600;
    margin-bottom: 0.6rem;
    font-size: 0.88rem;
    display: flex;
    align-items: center;
    gap: 0.4rem;
}

.topic-box ul { padding-left: 1.2rem; }

.topic-box li {
    margin-bottom: 0.4rem;
    font-size: 0.9rem;
    color: var(--text2);
    line-height: 1.55;
}

/* ── Flashcard ── */
.flashcard-container { perspective: 1000px; margin-bottom: 0.8rem; }

.flashcard {
    min-height: 200px;
    position: relative;
    transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
    transform-style: preserve-3d;
    cursor: pointer;
}

.flashcard.flipped { transform: rotateY(180deg); }

.flashcard .face {
    position: absolute;
    inset: 0;
    backface-visibility: hidden;
    border-radius: var(--radius);
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    text-align: center;
}

.flashcard .front-face {
    background: linear-gradient(135deg, var(--bg), var(--card));
    border: 1px solid var(--card-border);
}

.flashcard .front-face .prompt {
    color: var(--muted);
    font-size: 0.8rem;
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    margin-bottom: 0.8rem;
}

.flashcard .front-face .question-text {
    font-weight: 700;
    font-size: 1.05rem;
    color: var(--text);
    line-height: 1.5;
}

.flashcard .back-face {
    background: linear-gradient(135deg, #1e3a5f, #0f766e);
    color: white;
    transform: rotateY(180deg);
    border: 1px solid transparent;
}

.flashcard .back-face .prompt {
    font-size: 0.8rem;
    opacity: 0.7;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    margin-bottom: 0.8rem;
}

.flashcard .back-face .answer-text {
    font-size: 1rem;
    line-height: 1.6;
    font-weight: 500;
}

.fc-counter {
    text-align: center;
    font-size: 0.8rem;
    color: var(--muted);
    margin-bottom: 0.5rem;
    font-weight: 500;
}

.fc-progress {
    height: 4px;
    background: var(--bg2);
    border-radius: 999px;
    margin-bottom: 1rem;
    overflow: hidden;
}

.fc-progress-bar {
    height: 100%;
    background: linear-gradient(90deg, var(--primary), var(--accent));
    border-radius: 999px;
    transition: width 0.4s ease;
}

/* ── Controls ── */
.controls {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
    justify-content: center;
}

button {
    border: none;
    border-radius: 10px;
    padding: 0.6rem 1rem;
    cursor: pointer;
    font-weight: 600;
    font-size: 0.88rem;
    font-family: inherit;
    transition: var(--transition);
    display: inline-flex;
    align-items: center;
    gap: 0.4rem;
}

button:active { transform: scale(0.96); }

.btn-primary { background: var(--primary); color: white; }
.btn-primary:hover { background: var(--primary-dark); box-shadow: 0 4px 14px rgba(59,130,246,0.3); }
.btn-secondary { background: var(--secondary); color: white; }
.btn-secondary:hover { background: #e11d48; }
.btn-ghost { background: var(--bg); color: var(--text); border: 1px solid var(--card-border); }
.btn-ghost:hover { background: var(--bg2); }
.btn-accent { background: var(--accent); color: white; }
.btn-accent:hover { background: #0891b2; }
.btn-ok { background: var(--ok); color: white; }
.btn-ok:hover { background: #059669; }

/* ── Pill ── */
.pill {
    font-size: 0.78rem;
    padding: 0.25rem 0.65rem;
    background: linear-gradient(135deg, rgba(6,182,212,0.1), rgba(139,92,246,0.1));
    color: var(--accent);
    border-radius: 999px;
    border: 1px solid rgba(6,182,212,0.2);
    font-weight: 600;
}

/* ── Quiz ── */
.quiz-toolbar {
    display: flex;
    gap: 0.5rem;
    align-items: center;
    flex-wrap: wrap;
}

.question-block {
    padding: 1rem 1.2rem;
    border: 1px solid var(--card-border);
    border-radius: var(--radius);
    margin-bottom: 0.8rem;
    background: var(--bg);
    transition: var(--transition);
}

.question-title {
    font-weight: 700;
    margin-bottom: 0.6rem;
    font-size: 0.92rem;
    color: var(--text);
}

.options { list-style: none; display: grid; gap: 0.4rem; }

.option {
    border: 1px solid var(--card-border);
    border-radius: 10px;
    background: var(--card);
    padding: 0.6rem 0.8rem;
    cursor: pointer;
    font-size: 0.88rem;
    transition: var(--transition);
    color: var(--text);
}

.option:hover { border-color: var(--primary); transform: translateX(4px); }

.option.selected {
    background: rgba(59,130,246,0.1);
    border-color: var(--primary);
    color: var(--primary-dark);
    font-weight: 600;
}

.option.correct {
    background: rgba(16,185,129,0.12);
    border-color: var(--ok);
    color: #065f46;
}

[data-theme="dark"] .option.correct { color: #6ee7b7; }

.option.incorrect {
    background: rgba(239,68,68,0.12);
    border-color: var(--bad);
    color: #991b1b;
}

[data-theme="dark"] .option.incorrect { color: #fca5a5; }

.feedback {
    margin-top: 0.4rem;
    font-size: 0.84rem;
    color: var(--text2);
    display: none;
    padding: 0.5rem 0.7rem;
    background: rgba(59,130,246,0.06);
    border-radius: 8px;
    border-left: 3px solid var(--primary);
}

.result {
    margin-top: 1rem;
    padding: 1rem 1.2rem;
    border-radius: var(--radius);
    font-weight: 600;
    background: linear-gradient(135deg, rgba(59,130,246,0.08), rgba(6,182,212,0.08));
    border: 1px solid rgba(59,130,246,0.2);
    color: var(--primary);
    font-size: 1rem;
    text-align: center;
}

.tips {
    margin-top: 0.5rem;
    font-size: 0.88rem;
    color: var(--text2);
    text-align: center;
}

/* ── Keyboard Hint ── */
.keyboard-hint {
    text-align: center;
    margin-top: 0.6rem;
    font-size: 0.78rem;
    color: var(--muted);
}

.keyboard-hint kbd {
    background: var(--bg2);
    border: 1px solid var(--card-border);
    border-radius: 4px;
    padding: 0.1rem 0.35rem;
    font-family: inherit;
    font-size: 0.75rem;
    font-weight: 600;
}

/* ── Footer ── */
footer {
    text-align: center;
    padding: 1.5rem 1rem;
    color: var(--muted);
    font-size: 0.82rem;
    border-top: 1px solid var(--card-border);
    margin-top: 2rem;
}

/* ── Scroll to top ── */
.scroll-top {
    position: fixed;
    bottom: 1.5rem;
    right: 1.5rem;
    width: 44px;
    height: 44px;
    border-radius: 50%;
    background: var(--primary);
    color: white;
    border: none;
    cursor: pointer;
    font-size: 1.2rem;
    display: grid;
    place-items: center;
    box-shadow: 0 4px 16px rgba(59,130,246,0.35);
    opacity: 0;
    transform: translateY(12px);
    transition: var(--transition);
    z-index: 50;
}

.scroll-top.visible { opacity: 1; transform: translateY(0); }
.scroll-top:hover { transform: translateY(-3px); }

/* ── Confetti Canvas ── */
#confetti-canvas {
    position: fixed;
    top: 0; left: 0;
    width: 100%; height: 100%;
    pointer-events: none;
    z-index: 100;
}

/* ── Responsive ── */
@media (max-width: 1024px) {
    .layout { grid-template-columns: 1fr; }
}

@media (max-width: 768px) {
    header { padding: 2rem 1rem 1.5rem; }
    .stats { grid-template-columns: repeat(2, 1fr); }
    .topic-list { grid-template-columns: 1fr; }
    .tab-btn { font-size: 0.82rem; padding: 0.6rem 0.7rem; }
    .card-head { flex-direction: column; align-items: flex-start; }
    .quiz-toolbar { width: 100%; }
}

@media (max-width: 480px) {
    .wrapper { padding: 1rem 0.8rem 2rem; }
    header h1 { font-size: 1.2rem; }
    .stats { grid-template-columns: 1fr 1fr; gap: 0.5rem; }
    .stat-card .value { font-size: 1.2rem; }
    .controls { flex-direction: column; }
    .controls button { width: 100%; justify-content: center; }
    .tab-nav { gap: 0.2rem; }
}

/* ── Smooth scroll ── */
html { scroll-behavior: smooth; }