* {
    box-sizing: border-box;
}

body.app-body {
    margin: 0;
    min-height: 100vh;
    font-family: "Segoe UI", "Hiragino Sans", "Hiragino Kaku Gothic ProN", Meiryo, sans-serif;
    background: linear-gradient(160deg, #0f172a 0%, #1e293b 45%, #334155 100%);
    color: #f8fafc;
}

.app {
    max-width: 720px;
    margin: 0 auto;
    padding: 2rem 1.25rem 3rem;
}

h1 {
    margin: 0 0 0.5rem;
    font-size: clamp(1.75rem, 4vw, 2.25rem);
    text-align: center;
}

.description {
    margin: 0 0 1.5rem;
    text-align: center;
    color: #cbd5e1;
    line-height: 1.6;
}

.score {
    margin: 0 0 1.25rem;
    padding: 0.75rem 1rem;
    border-radius: 0.75rem;
    background: rgba(15, 23, 42, 0.55);
    border: 1px solid rgba(148, 163, 184, 0.25);
    text-align: center;
    font-weight: 600;
}

.color-box {
    width: 100%;
    height: 220px;
    border-radius: 1rem;
    border: 3px solid rgba(248, 250, 252, 0.85);
    box-shadow: 0 16px 40px rgba(0, 0, 0, 0.35);
    margin-bottom: 1.5rem;
}

.choices {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 0.75rem;
    margin-bottom: 1rem;
}

.choice-button {
    padding: 0.9rem 0.75rem;
    border: 2px solid rgba(148, 163, 184, 0.45);
    border-radius: 0.75rem;
    background: rgba(15, 23, 42, 0.75);
    color: #f8fafc;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: transform 0.15s ease, border-color 0.15s ease, background 0.15s ease;
}

.choice-button:hover:not(:disabled) {
    transform: translateY(-2px);
    border-color: #38bdf8;
    background: rgba(30, 41, 59, 0.95);
}

.choice-button:disabled {
    cursor: default;
    opacity: 0.95;
}

.choice-button.correct-choice {
    border-color: #22c55e;
    background: rgba(22, 101, 52, 0.55);
}

.choice-button.wrong-choice {
    border-color: #ef4444;
    background: rgba(127, 29, 29, 0.55);
}

.feedback {
    min-height: 1.5rem;
    margin: 0 0 1rem;
    text-align: center;
    font-weight: 700;
}

.feedback.correct {
    color: #4ade80;
}

.feedback.incorrect {
    color: #f87171;
}

.next-button {
    display: block;
    width: 100%;
    padding: 0.9rem 1rem;
    border: none;
    border-radius: 0.75rem;
    background: linear-gradient(135deg, #2563eb, #7c3aed);
    color: #fff;
    font-size: 1rem;
    font-weight: 700;
    cursor: pointer;
    transition: opacity 0.15s ease, transform 0.15s ease;
}

.next-button:hover:not(:disabled) {
    transform: translateY(-1px);
}

.next-button:disabled {
    opacity: 0.45;
    cursor: not-allowed;
}

.footer {
    margin-top: 1.5rem;
    text-align: center;
    color: #94a3b8;
    font-size: 0.85rem;
}

@media (max-width: 520px) {
    .choices {
        grid-template-columns: 1fr;
    }

    .color-box {
        height: 180px;
    }
}