/* ===========================
   Math Quiz — Stylesheet
   =========================== */

:root {
    --color-primary: #4361ee;
    --color-primary-hover: #3a56d4;
    --color-success: #2ec4b6;
    --color-danger: #e63946;
    --color-warning: #f4a261;
    --color-bg: #f0f4ff;
    --color-card: #ffffff;
    --color-text: #2b2d42;
    --color-text-light: #6c757d;
    --color-border: #dee2e6;
    --radius: 12px;
    --shadow: 0 4px 16px rgba(0, 0, 0, 0.08);
}

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

body {
    font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
    background: var(--color-bg);
    color: var(--color-text);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    padding: 1rem;
}

.container {
    max-width: 600px;
    width: 100%;
}

/* Title */
.app-title {
    text-align: center;
    font-size: 2rem;
    margin: 1rem 0 1.5rem;
    color: var(--color-primary);
}

/* Screens */
.screen[hidden] {
    display: none !important;
}

/* Card */
.card {
    background: var(--color-card);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    padding: 1.5rem;
    margin-bottom: 1.5rem;
}

.card h2 {
    text-align: center;
    margin-bottom: 1.25rem;
    font-size: 1.5rem;
    color: var(--color-primary);
}

/* Settings */
.setting-group {
    margin-bottom: 1.25rem;
}

.setting-group > label {
    display: block;
    font-weight: 600;
    margin-bottom: 0.4rem;
    font-size: 1rem;
}

.setting-group input[type="number"] {
    width: 100%;
    padding: 0.6rem 0.8rem;
    border: 2px solid var(--color-border);
    border-radius: 8px;
    font-size: 1.1rem;
    transition: border-color 0.2s;
}

.setting-group input[type="number"]:focus {
    outline: none;
    border-color: var(--color-primary);
}

/* Radio group */
.radio-group {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
}

.radio-label {
    display: flex;
    align-items: center;
    gap: 0.35rem;
    padding: 0.5rem 0.9rem;
    border: 2px solid var(--color-border);
    border-radius: 8px;
    cursor: pointer;
    font-size: 0.95rem;
    transition: all 0.2s;
}

.radio-label:has(input:checked) {
    border-color: var(--color-primary);
    background: #eef0fb;
}

.radio-label input[type="radio"] {
    accent-color: var(--color-primary);
}

.operation-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 0.4rem;
}

.operation-checkbox {
    display: flex;
    align-items: center;
    gap: 0.3rem;
    padding: 0.5rem 0.7rem;
    border: 2px solid var(--color-border);
    border-radius: 8px;
    cursor: pointer;
    font-size: 0.95rem;
    font-weight: 600;
    transition: all 0.2s;
    user-select: none;
}

.operation-checkbox:has(input:checked) {
    border-color: var(--color-primary);
    background: #eef0fb;
    color: var(--color-primary);
}

.operation-checkbox input[type="checkbox"] {
    accent-color: var(--color-primary);
}

/* Number grid */
.checkbox-actions {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 0.5rem;
}

.number-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 0.4rem;
}

.number-checkbox {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.3rem;
    padding: 0.5rem;
    border: 2px solid var(--color-border);
    border-radius: 8px;
    cursor: pointer;
    font-size: 1.1rem;
    font-weight: 600;
    transition: all 0.2s;
    user-select: none;
}

.number-checkbox:has(input:checked) {
    border-color: var(--color-primary);
    background: #eef0fb;
    color: var(--color-primary);
}

.number-checkbox input[type="checkbox"] {
    accent-color: var(--color-primary);
}

/* Buttons */
.btn-primary {
    display: block;
    width: 100%;
    padding: 0.85rem;
    font-size: 1.2rem;
    font-weight: 700;
    color: #fff;
    background: var(--color-primary);
    border: none;
    border-radius: 8px;
    cursor: pointer;
    transition: background 0.2s, transform 0.1s;
}

.btn-primary:hover {
    background: var(--color-primary-hover);
}

.btn-primary:active {
    transform: scale(0.98);
}

.btn-small {
    padding: 0.35rem 0.75rem;
    font-size: 0.85rem;
    font-weight: 600;
    border: 2px solid var(--color-border);
    border-radius: 6px;
    background: #fff;
    cursor: pointer;
    transition: all 0.2s;
}

.btn-small:hover {
    border-color: var(--color-primary);
    color: var(--color-primary);
}

.btn-secondary {
    color: var(--color-text-light);
}

/* Error message */
.error-message {
    color: var(--color-danger);
    font-weight: 600;
    text-align: center;
    margin-bottom: 0.75rem;
    font-size: 0.95rem;
}

/* Quiz screen */
.quiz-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
    padding: 0 0.25rem;
}

.progress {
    font-size: 1rem;
    font-weight: 600;
    color: var(--color-text-light);
}

.timer {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--color-primary);
    font-variant-numeric: tabular-nums;
}

.timer.warning {
    color: var(--color-warning);
}

.timer.danger {
    color: var(--color-danger);
    animation: pulse 0.5s ease-in-out infinite alternate;
}

@keyframes pulse {
    from { opacity: 1; }
    to { opacity: 0.5; }
}

.quiz-card {
    text-align: center;
}

.problem-display {
    margin: 1.5rem 0;
}

.problem-text {
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--color-text);
    letter-spacing: 0.04em;
}

.answer-area {
    display: flex;
    gap: 0.75rem;
    justify-content: center;
    align-items: center;
    margin-bottom: 0.75rem;
}

.answer-input {
    width: 120px;
    padding: 0.7rem;
    font-size: 1.8rem;
    font-weight: 700;
    text-align: center;
    border: 3px solid var(--color-border);
    border-radius: 8px;
    transition: border-color 0.2s;
    -moz-appearance: textfield;
}

.answer-input::-webkit-inner-spin-button,
.answer-input::-webkit-outer-spin-button {
    -webkit-appearance: none;
    margin: 0;
}

.answer-input:focus {
    outline: none;
    border-color: var(--color-primary);
}

.answer-area .btn-primary {
    width: auto;
    padding: 0.7rem 1.5rem;
    font-size: 1.1rem;
}

.skip-area {
    margin-top: 0.25rem;
}

/* Results screen */
.score-summary {
    text-align: center;
    margin-bottom: 1.5rem;
}

.score-big {
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--color-primary);
}

.score-percent {
    font-size: 1.3rem;
    font-weight: 600;
    color: var(--color-text-light);
    margin-top: 0.25rem;
}

.score-time {
    font-size: 1rem;
    color: var(--color-text-light);
    margin-top: 0.25rem;
}

.results-table-container {
    max-height: 400px;
    overflow-y: auto;
    margin-bottom: 1.25rem;
    border-radius: 8px;
    border: 1px solid var(--color-border);
}

.results-table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.95rem;
}

.results-table th {
    background: var(--color-bg);
    position: sticky;
    top: 0;
    font-weight: 600;
    text-align: left;
    padding: 0.6rem 0.75rem;
    border-bottom: 2px solid var(--color-border);
}

.results-table td {
    padding: 0.5rem 0.75rem;
    border-bottom: 1px solid var(--color-border);
}

.results-table tr:last-child td {
    border-bottom: none;
}

.results-table .correct {
    color: var(--color-success);
    font-weight: 700;
}

.results-table .incorrect {
    color: var(--color-danger);
    font-weight: 700;
}

.results-table .skipped {
    color: var(--color-text-light);
    font-style: italic;
}

/* Responsive */
@media (max-width: 480px) {
    .app-title {
        font-size: 1.6rem;
    }

    .number-grid {
        grid-template-columns: repeat(3, 1fr);
    }

    .problem-text {
        font-size: 2rem;
    }

    .answer-input {
        width: 90px;
        font-size: 1.4rem;
    }

    .results-table {
        font-size: 0.85rem;
    }

    .results-table th,
    .results-table td {
        padding: 0.4rem 0.5rem;
    }
}