:root {
    --primary-color: #0052CC;
    --primary-hover: #0747A6;
    --secondary-color: #42526E;
    --background-color: #F4F5F7;
    --surface-color: #FFFFFF;
    --text-primary: #172B4D;
    --text-secondary: #5E6C84;
    --border-color: #DFE1E6;
    --success-color: #00875A;
    --danger-color: #DE350B;
    --shadow-sm: 0 1px 1px rgba(9, 30, 66, 0.13);
    --shadow-md: 0 4px 8px -2px rgba(9, 30, 66, 0.13);
    --shadow-lg: 0 8px 16px -4px rgba(9, 30, 66, 0.13);
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, 'Fira Sans', 'Droid Sans', 'Helvetica Neue', sans-serif;
    background-color: var(--background-color);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.container {
    max-width: 1200px;
    width: 100%;
    margin: 0 auto;
    padding: 0 20px;
    flex: 1;
    display: flex;
    flex-direction: column;
}

header {
    background-color: var(--surface-color);
    padding: 24px 0;
    box-shadow: var(--shadow-sm);
    position: relative;
    margin-bottom: 32px;
}

h1 {
    font-size: 32px;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 8px;
    text-align: center;
}

.subtitle {
    text-align: center;
    color: var(--text-secondary);
    font-size: 16px;
}

.language-selector {
    position: absolute;
    top: 24px;
    right: 20px;
}

#language-select {
    padding: 8px 16px;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    background-color: var(--surface-color);
    color: var(--text-primary);
    font-size: 14px;
    cursor: pointer;
    transition: all 0.2s ease;
}

#language-select:hover {
    border-color: var(--primary-color);
}

main {
    flex: 1;
}

.sound-selector {
    background-color: var(--surface-color);
    padding: 32px;
    border-radius: 8px;
    box-shadow: var(--shadow-md);
    margin-bottom: 24px;
}

.sound-selector h2 {
    font-size: 20px;
    font-weight: 500;
    margin-bottom: 24px;
    color: var(--text-primary);
}

.sound-buttons {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 16px;
}

.sound-btn {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 8px;
    padding: 20px;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    background-color: var(--surface-color);
    cursor: pointer;
    transition: all 0.2s ease;
    font-size: 14px;
    color: var(--text-primary);
}

.sound-btn:hover {
    border-color: var(--primary-color);
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.sound-btn.active {
    border-color: var(--primary-color);
    background-color: #DEEBFF;
}

.sound-btn .icon {
    font-size: 32px;
}

.controls {
    background-color: var(--surface-color);
    padding: 32px;
    border-radius: 8px;
    box-shadow: var(--shadow-md);
    margin-bottom: 24px;
}

.control-group {
    margin-bottom: 24px;
}

.control-group label {
    display: block;
    font-weight: 500;
    margin-bottom: 8px;
    color: var(--text-primary);
}

#volume-slider {
    width: 100%;
    height: 6px;
    border-radius: 3px;
    background: var(--border-color);
    outline: none;
    -webkit-appearance: none;
}

#volume-slider::-webkit-slider-thumb {
    -webkit-appearance: none;
    appearance: none;
    width: 20px;
    height: 20px;
    border-radius: 50%;
    background: var(--primary-color);
    cursor: pointer;
    transition: all 0.2s ease;
}

#volume-slider::-webkit-slider-thumb:hover {
    background: var(--primary-hover);
    transform: scale(1.1);
}

#volume-slider::-moz-range-thumb {
    width: 20px;
    height: 20px;
    border-radius: 50%;
    background: var(--primary-color);
    cursor: pointer;
    border: none;
    transition: all 0.2s ease;
}

#volume-slider::-moz-range-thumb:hover {
    background: var(--primary-hover);
    transform: scale(1.1);
}

#volume-value {
    display: inline-block;
    margin-left: 16px;
    font-weight: 500;
    color: var(--primary-color);
}

#timer-select {
    padding: 10px 16px;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    background-color: var(--surface-color);
    color: var(--text-primary);
    font-size: 14px;
    cursor: pointer;
    width: 200px;
    transition: all 0.2s ease;
}

#timer-select:hover {
    border-color: var(--primary-color);
}

.timer-display {
    margin-left: 16px;
    font-weight: 500;
    color: var(--primary-color);
    display: none;
}

.play-controls {
    display: flex;
    gap: 16px;
    justify-content: center;
}

.play-btn,
.stop-btn {
    width: 64px;
    height: 64px;
    border-radius: 50%;
    border: none;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.2s ease;
    color: white;
}

.play-btn {
    background-color: var(--success-color);
}

.play-btn:hover:not(:disabled) {
    background-color: #006644;
    transform: scale(1.05);
}

.play-btn:disabled {
    background-color: var(--border-color);
    cursor: not-allowed;
}

.stop-btn {
    background-color: var(--danger-color);
}

.stop-btn:hover:not(:disabled) {
    background-color: #BF2600;
    transform: scale(1.05);
}

.stop-btn:disabled {
    background-color: var(--border-color);
    cursor: not-allowed;
}

.info-section {
    background-color: var(--surface-color);
    padding: 32px;
    border-radius: 8px;
    box-shadow: var(--shadow-md);
    margin-bottom: 32px;
}

.info-section h3 {
    font-size: 20px;
    font-weight: 500;
    margin-bottom: 16px;
    color: var(--text-primary);
}

.benefits-list {
    list-style: none;
}

.benefits-list li {
    padding: 12px 0;
    padding-left: 28px;
    position: relative;
    color: var(--text-secondary);
    border-bottom: 1px solid var(--border-color);
}

.benefits-list li:last-child {
    border-bottom: none;
}

.benefits-list li::before {
    content: '✓';
    position: absolute;
    left: 0;
    color: var(--success-color);
    font-weight: bold;
    font-size: 18px;
}

footer {
    background-color: var(--surface-color);
    padding: 24px 0;
    text-align: center;
    box-shadow: 0 -1px 1px rgba(9, 30, 66, 0.13);
    margin-top: auto;
}

footer p {
    color: var(--text-secondary);
    font-size: 14px;
}

/* レスポンシブデザイン */
@media (max-width: 768px) {
    .container {
        padding: 0 16px;
    }
    
    header {
        padding: 16px 0;
    }
    
    h1 {
        font-size: 24px;
    }
    
    .subtitle {
        font-size: 14px;
    }
    
    .language-selector {
        position: static;
        text-align: center;
        margin-top: 16px;
    }
    
    .sound-selector,
    .controls,
    .info-section {
        padding: 24px;
    }
    
    .sound-buttons {
        grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
        gap: 12px;
    }
    
    .sound-btn {
        padding: 16px;
        font-size: 12px;
    }
    
    .sound-btn .icon {
        font-size: 24px;
    }
    
    #timer-select {
        width: 100%;
    }
    
    .play-btn,
    .stop-btn {
        width: 56px;
        height: 56px;
    }
}

/* アニメーション */
@keyframes pulse {
    0% {
        box-shadow: 0 0 0 0 rgba(0, 135, 90, 0.4);
    }
    70% {
        box-shadow: 0 0 0 20px rgba(0, 135, 90, 0);
    }
    100% {
        box-shadow: 0 0 0 0 rgba(0, 135, 90, 0);
    }
}

.play-btn:not(:disabled) {
    animation: pulse 2s infinite;
}

/* アクセシビリティ */
:focus {
    outline: 2px solid var(--primary-color);
    outline-offset: 2px;
}

/* ダークモード対応（システム設定に従う） */
@media (prefers-color-scheme: dark) {
    :root {
        --background-color: #1B1F23;
        --surface-color: #24292E;
        --text-primary: #F0F6FC;
        --text-secondary: #8B949E;
        --border-color: #30363D;
    }
    
    .sound-btn.active {
        background-color: #1F2937;
    }
}