/* ─── Variables ─────────────────────────────────────────────── */
:root {
    --primary:       #c62828;
    --primary-light: #ef5350;
    --accent:        #f9a825;
    --accent-light:  #ffd54f;
    --text:          #1a1a2e;
    --text-muted:    #6b7280;
    --bg:            #f4f5f7;
    --surface:       #ffffff;
    --surface-alt:   #fafafa;
    --border:        #e5e7eb;
    --shadow-sm:     0 1px 3px rgba(0,0,0,0.08), 0 1px 2px rgba(0,0,0,0.06);
    --shadow:        0 4px 12px rgba(0,0,0,0.08), 0 2px 4px rgba(0,0,0,0.05);
    --shadow-lg:     0 10px 30px rgba(0,0,0,0.12), 0 4px 10px rgba(0,0,0,0.07);
    --radius-sm:     0.375rem;
    --radius:        0.75rem;
    --radius-lg:     1.25rem;
    --transition:    0.2s ease;
}

/* ─── Reset & Base ───────────────────────────────────────────── */
*, *::before, *::after {
    box-sizing: border-box;
}

body {
    font-family: 'Inter', 'Segoe UI', sans-serif;
    background-color: var(--bg);
    color: var(--text);
    margin: 0;
    padding: 16px;
    min-height: 100vh;
    display: flex;
    justify-content: center;
}

/* Chinese text uses Noto Sans SC for proper glyph rendering */
h2, .card-front h2, .card-back h2,
#card-chinese, #card-meaning {
    font-family: 'Noto Sans SC', 'PingFang SC', 'Microsoft YaHei', sans-serif;
}

.container {
    width: 100%;
    max-width: 820px;
}

/* ─── Header ─────────────────────────────────────────────────── */
header {
    text-align: center;
    margin-bottom: 28px;
    padding: 0 4px;
}

h1 {
    color: var(--primary);
    font-size: clamp(1.5rem, 5vw, 2.25rem);
    font-weight: 700;
    letter-spacing: -0.02em;
    margin: 0 0 20px;
}

/* ─── Navigation ─────────────────────────────────────────────── */
nav {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
    justify-content: center;
}

nav button {
    background: var(--surface);
    border: 2px solid var(--primary);
    color: var(--primary);
    padding: 10px 18px;
    border-radius: 999px;
    cursor: pointer;
    font-family: inherit;
    font-size: 0.875rem;
    font-weight: 600;
    transition: background var(--transition), color var(--transition),
                box-shadow var(--transition), transform var(--transition);
    white-space: nowrap;
    min-height: 44px;
}

nav button:hover {
    background: var(--primary);
    color: #fff;
    box-shadow: 0 4px 12px rgba(198,40,40,0.3);
    transform: translateY(-1px);
}

nav button.active {
    background: var(--primary);
    color: #fff;
    box-shadow: 0 4px 12px rgba(198,40,40,0.25);
}

/* ─── Sections ───────────────────────────────────────────────── */
.section {
    background: var(--surface);
    padding: 28px;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow);
}

.hidden {
    display: none !important;
}

/* ─── Study Mode ─────────────────────────────────────────────── */
.lesson-selector {
    margin-bottom: 24px;
    text-align: center;
}

.lesson-selector label {
    display: block;
    font-size: 0.85rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-muted);
    margin-bottom: 8px;
}

#lesson-select {
    padding: 10px 16px;
    border-radius: var(--radius);
    border: 2px solid var(--border);
    font-family: inherit;
    font-size: 0.95rem;
    color: var(--text);
    background: var(--surface);
    cursor: pointer;
    transition: border-color var(--transition), box-shadow var(--transition);
    max-width: 100%;
}

#lesson-select:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(198,40,40,0.12);
}

/* ─── Flashcard ──────────────────────────────────────────────── */
.flashcard-container {
    display: flex;
    flex-direction: column;
    align-items: center;
    perspective: 1200px;
    padding: 8px 0;
}

.flashcard {
    width: min(300px, 88vw);
    height: min(400px, 60vh);
    position: relative;
    transform-style: preserve-3d;
    transition: transform 0.55s cubic-bezier(0.4, 0, 0.2, 1),
                box-shadow var(--transition);
    cursor: pointer;
    box-shadow: var(--shadow);
    border-radius: var(--radius-lg);
}

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

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

.card-front, .card-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    -webkit-backface-visibility: hidden;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    border-radius: var(--radius-lg);
    text-align: center;
    padding: 24px;
}

.card-front {
    background: linear-gradient(145deg, #ffffff 0%, #fdf7f7 100%);
    border: 1px solid var(--border);
}

.card-back {
    transform: rotateY(180deg);
    background: linear-gradient(145deg, var(--accent) 0%, #e65100 100%);
    color: #fff;
}

.card-front .emoji {
    font-size: clamp(2.5rem, 8vw, 4rem);
    margin-bottom: 16px;
    line-height: 1;
}

.card-front h2 {
    font-size: clamp(2rem, 7vw, 3rem);
    margin: 8px 0;
    color: var(--text);
    line-height: 1.1;
}

.card-front p {
    font-size: clamp(1rem, 3.5vw, 1.2rem);
    color: var(--text-muted);
    margin: 4px 0 0;
}

.card-back h2 {
    font-size: clamp(1.4rem, 5vw, 2rem);
    color: #fff;
    font-weight: 700;
}

/* ─── Card Controls ──────────────────────────────────────────── */
.controls {
    margin-top: 24px;
    display: flex;
    gap: 16px;
    align-items: center;
}

.controls button {
    padding: 10px 22px;
    background: var(--primary);
    color: #fff;
    border: none;
    border-radius: var(--radius);
    cursor: pointer;
    font-family: inherit;
    font-size: 0.9rem;
    font-weight: 600;
    min-height: 44px;
    transition: background var(--transition), transform var(--transition),
                box-shadow var(--transition);
}

.controls button:hover {
    background: var(--primary-light);
    transform: translateY(-1px);
    box-shadow: 0 4px 10px rgba(198,40,40,0.25);
}

.controls button:active {
    transform: translateY(0);
}

#card-counter {
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-muted);
    min-width: 56px;
    text-align: center;
}

/* ─── Grammar Review ─────────────────────────────────────────── */
.grammar-lesson {
    margin-bottom: 40px;
}

.grammar-lesson h3 {
    border-bottom: 2px solid var(--accent-light);
    padding-bottom: 10px;
    color: var(--primary);
    font-size: 1.1rem;
    font-weight: 700;
}

.rule-card {
    background: var(--surface-alt);
    border: 1px solid var(--border);
    border-left: 4px solid var(--primary);
    padding: 16px 18px;
    margin: 12px 0;
    border-radius: 0 var(--radius) var(--radius) 0;
    transition: box-shadow var(--transition), transform var(--transition);
}

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

.rule-card strong {
    display: block;
    margin-bottom: 6px;
    font-size: 1rem;
    color: var(--text);
}

/* ─── Measure Words ──────────────────────────────────────────── */
.measure-card {
    background: var(--surface-alt);
    border: 1px solid var(--border);
    border-left: 4px solid var(--accent);
    padding: 16px 18px;
    margin: 12px 0;
    border-radius: 0 var(--radius) var(--radius) 0;
    transition: box-shadow var(--transition), transform var(--transition);
}

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

/* ─── Practice Mode ──────────────────────────────────────────── */
#test-intro {
    text-align: center;
    padding: 20px 0;
}

#test-intro p {
    color: var(--text-muted);
    font-size: 1rem;
    line-height: 1.6;
    margin-bottom: 24px;
}

#test-intro button,
#test-results button {
    padding: 12px 32px;
    background: var(--primary);
    color: #fff;
    border: none;
    border-radius: 999px;
    cursor: pointer;
    font-family: inherit;
    font-size: 1rem;
    font-weight: 600;
    min-height: 48px;
    transition: background var(--transition), transform var(--transition),
                box-shadow var(--transition);
}

#test-intro button:hover,
#test-results button:hover {
    background: var(--primary-light);
    transform: translateY(-1px);
    box-shadow: 0 6px 16px rgba(198,40,40,0.3);
}

#test-timer {
    text-align: right;
    font-weight: 700;
    color: var(--primary);
    font-size: 1.1rem;
    margin-bottom: 20px;
    position: sticky;
    top: 0;
    background: var(--surface);
    padding: 10px 0;
    z-index: 10;
    border-bottom: 1px solid var(--border);
}

.test-part {
    margin-bottom: 36px;
    border-bottom: 1px solid var(--border);
    padding-bottom: 28px;
}

.test-part:last-of-type {
    border-bottom: none;
}

.test-part h3 {
    color: var(--primary);
    font-size: 1.05rem;
    font-weight: 700;
    margin-bottom: 16px;
}

.question {
    margin: 18px 0;
    line-height: 1.5;
}

.options label {
    display: flex;
    align-items: center;
    gap: 8px;
    margin: 10px 0;
    padding: 8px 12px;
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: background var(--transition);
}

.options label:hover {
    background: #fef2f2;
}

.options input[type="radio"] {
    accent-color: var(--primary);
    width: 16px;
    height: 16px;
    flex-shrink: 0;
}

.pinyin-input, .fill-input {
    padding: 9px 12px;
    border: 2px solid var(--border);
    border-radius: var(--radius-sm);
    font-family: inherit;
    font-size: 0.95rem;
    width: 200px;
    transition: border-color var(--transition), box-shadow var(--transition);
}

.pinyin-input:focus, .fill-input:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(198,40,40,0.1);
}

.audio-btn {
    background: none;
    border: none;
    cursor: pointer;
    font-size: 1.4rem;
    margin-right: 8px;
    padding: 4px;
    transition: transform var(--transition);
}

.audio-btn:hover {
    transform: scale(1.15);
}

.match-item {
    display: flex;
    align-items: center;
    gap: 10px;
    margin: 10px 0;
    flex-wrap: wrap;
}

.emoji-pic {
    font-size: 1.8rem;
}

.match-item select {
    padding: 8px 12px;
    border: 2px solid var(--border);
    border-radius: var(--radius-sm);
    font-family: inherit;
    font-size: 0.9rem;
    cursor: pointer;
    transition: border-color var(--transition);
}

.match-item select:focus {
    outline: none;
    border-color: var(--primary);
}

/* Submit button inside test form */
#test-form > button[type="button"] {
    display: block;
    margin: 24px auto 0;
    padding: 12px 40px;
    background: var(--primary);
    color: #fff;
    border: none;
    border-radius: 999px;
    cursor: pointer;
    font-family: inherit;
    font-size: 1rem;
    font-weight: 600;
    min-height: 48px;
    transition: background var(--transition), transform var(--transition),
                box-shadow var(--transition);
}

#test-form > button[type="button"]:hover {
    background: var(--primary-light);
    transform: translateY(-1px);
    box-shadow: 0 6px 16px rgba(198,40,40,0.3);
}

/* ─── Results ────────────────────────────────────────────────── */
#test-results {
    text-align: center;
}

#test-results h2 {
    color: var(--primary);
    font-size: 1.5rem;
    margin-bottom: 8px;
}

#final-score {
    font-size: clamp(1.6rem, 5vw, 2.2rem);
    font-weight: 700;
    margin: 16px 0 24px;
    color: var(--text);
}

#results-summary {
    text-align: left;
    margin: 0 auto 24px;
    max-width: 560px;
}

.result-item {
    padding: 10px 14px;
    margin: 6px 0;
    border-radius: var(--radius-sm);
    font-size: 0.9rem;
    background: var(--surface-alt);
    border: 1px solid var(--border);
}

.correct {
    color: #16a34a;
    font-weight: 600;
}

.incorrect {
    color: #dc2626;
    font-weight: 600;
}

/* ─── Mobile — ≤600px ────────────────────────────────────────── */
@media (max-width: 600px) {
    body {
        padding: 12px 10px;
    }

    .section {
        padding: 18px 14px;
        border-radius: var(--radius);
    }

    nav {
        display: grid;
        grid-template-columns: 1fr 1fr;
        gap: 8px;
        width: 100%;
    }

    nav button {
        width: 100%;
        padding: 10px 8px;
        font-size: 0.82rem;
        border-radius: var(--radius-sm);
        text-align: center;
    }

    h1 {
        margin-bottom: 16px;
    }

    .controls {
        gap: 10px;
    }

    .controls button {
        padding: 10px 16px;
        font-size: 0.85rem;
    }

    .pinyin-input, .fill-input {
        width: 100%;
        max-width: 100%;
    }

    .match-item select {
        flex: 1;
        min-width: 0;
    }

    .options label {
        padding: 10px 10px;
    }

    #test-timer {
        font-size: 1rem;
        padding: 8px 0;
    }

    .test-part h3 {
        font-size: 1rem;
    }

    #final-score {
        font-size: 1.6rem;
    }

    .question {
        font-size: 0.95rem;
    }
}

/* ─── Tablet — ≤768px ────────────────────────────────────────── */
@media (max-width: 768px) {
    .section {
        padding: 22px 18px;
    }

    .pinyin-input, .fill-input {
        width: 100%;
        max-width: 280px;
    }
}