body.lesson-body {
    margin: 0;
    font-family: "Noto Sans TC", "PingFang TC", "Microsoft JhengHei", sans-serif;
    color: #1f2937;
    background:
        radial-gradient(circle at top left, rgba(125, 211, 252, 0.28), transparent 28%),
        radial-gradient(circle at top right, rgba(251, 191, 36, 0.20), transparent 26%),
        linear-gradient(180deg, #f7fbff 0%, #eef6ff 100%);
}

.lesson-shell {
    max-width: 1080px;
    margin: 0 auto;
    padding: 32px 20px 48px;
}

.lesson-hero {
    padding: 32px;
    border-radius: 28px;
    background: linear-gradient(135deg, #0f3d66 0%, #0b7799 62%, #49b6b6 100%);
    color: #f8fafc;
    box-shadow: 0 20px 40px rgba(15, 61, 102, 0.18);
}

.lesson-hero a {
    color: #dbeafe;
}

.eyebrow {
    margin: 0 0 10px;
    font-size: 0.95rem;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    opacity: 0.82;
}

.lesson-hero h1 {
    margin: 0;
    font-size: clamp(2rem, 4vw, 3.2rem);
    line-height: 1.15;
}

.lesson-hero p {
    max-width: 760px;
    margin: 14px 0 0;
    font-size: 1.05rem;
}

.lesson-grid {
    display: grid;
    grid-template-columns: 1.2fr 0.8fr;
    gap: 24px;
    margin-top: 24px;
}

.panel {
    background: rgba(255, 255, 255, 0.92);
    border: 1px solid rgba(148, 163, 184, 0.22);
    border-radius: 24px;
    padding: 24px;
    box-shadow: 0 16px 30px rgba(148, 163, 184, 0.12);
}

.panel h2 {
    margin-top: 0;
    color: #0f4c81;
}

.panel h3 {
    color: #155e75;
}

.concept-list,
.tip-list {
    padding-left: 1.2rem;
}

.concept-list li,
.tip-list li {
    margin-bottom: 0.6rem;
}

.formula-box,
.example-box,
.quiz-box,
.summary-box {
    margin-top: 18px;
    border-radius: 18px;
    padding: 18px 20px;
}

.formula-box {
    background: #eff6ff;
    border-left: 6px solid #2563eb;
}

.example-box {
    background: #ecfeff;
    border-left: 6px solid #0d9488;
}

.summary-box {
    background: #fefce8;
    border-left: 6px solid #ca8a04;
}

.cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(190px, 1fr));
    gap: 14px;
    margin-top: 18px;
}

.card {
    background: #ffffff;
    border: 1px solid #dbeafe;
    border-radius: 18px;
    padding: 16px;
}

.card strong {
    display: block;
    margin-bottom: 8px;
    color: #1d4ed8;
}

.visual-frame {
    margin-top: 18px;
    background: linear-gradient(180deg, #ffffff 0%, #f8fbff 100%);
    border: 1px solid #d7e6f7;
    border-radius: 24px;
    padding: 16px;
}

.visual-frame svg {
    width: 100%;
    height: auto;
    display: block;
}

.caption {
    margin: 12px 0 0;
    color: #475569;
    font-size: 0.95rem;
}

.quiz-box {
    background: #fffdf2;
    border: 2px dashed #f59e0b;
}

.quiz-box h3 {
    margin-top: 0;
}

.quiz-question {
    font-size: 1.08rem;
    margin: 12px 0;
}

.quiz-input-row {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    align-items: center;
    margin: 12px 0;
}

.quiz-input-row label {
    font-weight: 600;
}

.quiz-input-row input,
.quiz-input-row select {
    min-width: 88px;
    padding: 10px 12px;
    border: 1px solid #cbd5e1;
    border-radius: 12px;
    font-size: 1rem;
}

.button-row {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    margin-top: 12px;
}

button {
    border: none;
    border-radius: 999px;
    padding: 10px 18px;
    cursor: pointer;
    font-size: 0.98rem;
    font-weight: 700;
    color: #fff;
    background: linear-gradient(135deg, #0f766e, #0ea5a4);
}

button.secondary {
    background: linear-gradient(135deg, #64748b, #94a3b8);
}

button:hover {
    opacity: 0.92;
}

.feedback {
    min-height: 24px;
    margin-top: 12px;
    padding: 12px 14px;
    border-radius: 14px;
    font-weight: 700;
}

.feedback:empty {
    padding: 0;
    min-height: 0;
}

.feedback.correct {
    background: #ecfdf5;
    color: #166534;
    border: 1px solid #86efac;
}

.feedback.incorrect {
    background: #fef2f2;
    color: #b91c1c;
    border: 1px solid #fca5a5;
}

.lesson-footer {
    text-align: center;
    color: #475569;
    margin-top: 32px;
}

@media (max-width: 860px) {
    .lesson-grid {
        grid-template-columns: 1fr;
    }

    .lesson-hero,
    .panel {
        padding: 22px;
    }
}