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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: linear-gradient(135deg, #f5f7fa 0%, #e4e8ec 100%);
    min-height: 100vh;
    padding: 20px;
    color: #1a1a2e;
}

.container {
    max-width: 900px;
    margin: 0 auto;
}

/* Header */
header {
    text-align: center;
    margin-bottom: 32px;
}

header h1 {
    font-size: 32px;
    font-weight: 800;
    margin-bottom: 8px;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

header p {
    color: #6b7280;
    font-size: 16px;
}

/* Tabs */
.tabs {
    display: flex;
    gap: 8px;
    margin-bottom: 24px;
    border-bottom: 2px solid #e5e7eb;
    padding-bottom: 12px;
}

.tab-btn {
    flex: 1;
    padding: 12px 16px;
    border: none;
    border-radius: 10px;
    background: #f3f4f6;
    color: #374151;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
    font-size: 14px;
}

.tab-btn:hover {
    background: #e5e7eb;
    transform: translateY(-2px);
}

.tab-btn.active {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    box-shadow: 0 4px 15px rgba(102, 126, 234, 0.3);
}

/* Sections */
.section {
    display: none;
    animation: fadeIn 0.4s ease;
}

.section.active {
    display: block;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Flashcard */
.flashcard {
    width: 100%;
    height: 280px;
    perspective: 1000px;
    cursor: pointer;
}

.card-inner {
    width: 100%;
    height: 100%;
    position: relative;
    transform-style: preserve-3d;
    transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
}

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

.card-front, .card-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: 16px;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    padding: 40px;
    box-shadow: 0 10px 40px rgba(0,0,0,0.1);
}

.card-front {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
}

.card-back {
    background: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
    color: white;
    transform: rotateY(180deg);
}

.hint {
    font-size: 13px;
    opacity: 0.8;
    margin-bottom: 16px;
}

.card-front h2 {
    font-size: 42px;
    font-weight: 700;
    margin: 0;
}

.card-front p {
    font-size: 18px;
    opacity: 0.9;
    margin-top: 8px;
}

.card-back h3 {
    font-size: 26px;
    margin-bottom: 12px;
    text-align: center;
}

.card-back p {
    font-size: 17px;
    opacity: 0.95;
    text-align: center;
    line-height: 1.5;
}

.example {
    margin-top: 16px !important;
    font-style: italic;
    opacity: 0.8 !important;
    font-size: 15px !important;
}

.card-controls {
    display: flex;
    justify-content: center;
    gap: 16px;
    margin-top: 20px;
}

.card-controls button, .next-btn, .new-btn {
    padding: 12px 28px;
    border: 2px solid #e5e7eb;
    border-radius: 10px;
    background: white;
    color: #374151;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s;
    font-size: 15px;
}

.card-controls button:hover, .next-btn:hover, .new-btn:hover {
    border-color: #667eea;
    color: #667eea;
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(102, 126, 234, 0.15);
}

/* Quiz */
.quiz-box {
    background: #fef3c7;
    border-radius: 16px;
    padding: 32px;
    border: 2px solid #fbbf24;
}

.quiz-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
}

.badge {
    background: #fbbf24;
    color: #92400e;
    padding: 6px 14px;
    border-radius: 20px;
    font-size: 14px;
    font-weight: 600;
}

.score {
    color: #92400e;
    font-weight: 700;
    font-size: 16px;
}

.quiz-question {
    font-size: 20px;
    color: #1f2937;
    margin-bottom: 24px;
    font-weight: 600;
    line-height: 1.5;
}

.quiz-options {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.quiz-btn {
    padding: 16px 20px;
    border: 2px solid #fcd34d;
    border-radius: 12px;
    background: white;
    text-align: left;
    font-size: 16px;
    cursor: pointer;
    transition: all 0.2s;
    font-weight: 500;
}

.quiz-btn:hover:not(.disabled) {
    background: #fffbeb;
    border-color: #f59e0b;
    transform: translateX(4px);
}

.quiz-btn.correct {
    background: #d1fae5 !important;
    border-color: #10b981 !important;
}

.quiz-btn.wrong {
    background: #fee2e2 !important;
    border-color: #ef4444 !important;
}

.quiz-btn.disabled {
    cursor: default;
    opacity: 0.9;
}

.feedback {
    margin-top: 16px;
    padding: 14px;
    border-radius: 10px;
    font-weight: 600;
    text-align: center;
    animation: slideIn 0.3s ease;
}

.feedback.correct {
    background: #d1fae5;
    color: #065f46;
}

.feedback.wrong {
    background: #fee2e2;
    color: #991b1b;
}

.hidden {
    display: none !important;
}

.next-btn {
    margin-top: 16px;
    background: #f59e0b !important;
    color: white !important;
    border-color: #f59e0b !important;
}

.next-btn:hover {
    background: #d97706 !important;
}

@keyframes slideIn {
    from { opacity: 0; transform: translateY(-5px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Daily Sentence */
.daily-box {
    background: #ecfdf5;
    border-radius: 16px;
    padding: 40px 32px;
    border: 2px solid #34d399;
    text-align: center;
}

.emoji {
    font-size: 48px;
    margin-bottom: 16px;
}

.sentence-cn {
    font-size: 22px;
    color: #065f46;
    font-weight: 600;
    margin-bottom: 12px;
    line-height: 1.6;
}

.sentence-en {
    font-size: 18px;
    color: #059669;
    font-style: italic;
    margin-bottom: 20px;
    line-height: 1.5;
}

.tags {
    display: flex;
    justify-content: center;
    gap: 12px;
    flex-wrap: wrap;
}

.tag {
    background: #d1fae5;
    color: #065f46;
    padding: 8px 16px;
    border-radius: 20px;
    font-size: 14px;
    font-weight: 500;
}

.new-btn {
    margin-top: 24px;
    background: #10b981 !important;
    color: white !important;
    border-color: #10b981 !important;
    font-size: 16px;
}

.new-btn:hover {
    background: #059669 !important;
    transform: translateY(-2px);
    box-shadow: 0 4px 15px rgba(16, 185, 129, 0.3);
}

/* Info Grid */
.info-grid {
    margin-top: 20px;
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 12px;
}

.info-card {
    background: #f0fdf4;
    border-radius: 12px;
    padding: 20px;
    border: 1px solid #bbf7d0;
}

.info-card h4 {
    font-size: 14px;
    color: #166534;
    font-weight: 600;
    margin-bottom: 8px;
}

.info-card p {
    font-size: 13px;
    color: #15803d;
    line-height: 1.5;
    margin: 0;
}

/* Footer */
footer {
    margin-top: 32px;
    text-align: center;
    color: #9ca3af;
    font-size: 14px;
    padding: 20px;
}

/* Responsive */
@media (max-width: 600px) {
    .tabs {
        flex-direction: column;
    }
    
    .info-grid {
        grid-template-columns: 1fr;
    }
    
    .card-front h2 {
        font-size: 32px;
    }
    
    header h1 {
        font-size: 26px;
    }
}
/* ==================== English Roots Flip Cards ==================== */

.root-container {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 20px;
    margin-top: 20px;
}


.root-card {
    width: 200px;
    height: 150px;
    perspective: 1000px;
    cursor: pointer;
}


.root-inner {
    width: 100%;
    height: 100%;
    position: relative;
    transition: transform 0.6s;
    transform-style: preserve-3d;
}


.root-card.flipped .root-inner {
    transform: rotateY(180deg);
}


.root-front,
.root-back {

    position: absolute;

    width: 100%;
    height: 100%;

    display: flex;
    flex-direction: column;

    justify-content: center;
    align-items: center;

    border-radius: 16px;

    backface-visibility: hidden;

    box-shadow: 0 10px 30px rgba(0,0,0,0.15);

}


.root-front {

    background: linear-gradient(
        135deg,
        #667eea,
        #764ba2
    );

    color:white;

}


.root-back {

    background:white;

    color:#333;

    transform:rotateY(180deg);

}


.root-front h2 {

    font-size:36px;

}


.root-back p {

    margin:8px;

    font-size:16px;

}
.root-word {
    margin: 15px 0;
    padding: 12px;
    border-radius: 8px;
    background: rgba(255, 255, 255, 0.7);
}

.root-word h3 {
    margin-bottom: 6px;
    font-size: 22px;
}

.root-word p {
    margin: 5px 0;
}

.root-back hr {
    margin: 15px 0;
}
/* 让词根卡片自动适应屏幕宽度 */

.root-container {

    display: grid;

    grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));

    gap: 20px;

    width: 100%;

    box-sizing: border-box;

}



/* 手机屏幕：改为单列 */

@media (max-width: 700px) {

    .root-container {

        grid-template-columns: 1fr;

    }



    .root-card {

        width: 100%;

        max-width: 100%;

        box-sizing: b
/* 词根上一页 / 下一页导航 */

.root-navigation {

    display: flex;

    align-items: center;

    justify-content: space-between;

    gap: 12px;

    width: 100%;

    margin-bottom: 20px;

    box-sizing: border-box;

}



.root-navigation button {

    padding: 10px 14px;

    border: none;

    border-radius: 8px;

    background: #6256d9;

    color: white;

    font-size: 14px;

    cursor: pointer;

}



.root-navigation button:disabled {

    background: #cccccc;

    cursor: not-allowed;

}



.root-navigation span {

    font-weight: bold;

    text-align: center;

}



@media (max-width: 500px) {

    .root-navigation {

        gap: 6px;

    }



    .root-navigation button {

        padding: 9px 8px;

        font-size: 12px;

    }

}order-box;

    }

}