:root {
    /* カラーパレット */
    --bg-color: #f4f6f8;
    --text-main: #2d3436;
    --text-muted: #636e72;
    --primary-color: #0984e3;
    --primary-hover: #74b9ff;
    --accent-warning: #fdcb6e;
    --accent-danger: #ff7675;
    --card-bg: #ffffff;
    --shadow-soft: 0 10px 25px rgba(0, 0, 0, 0.05);
    --shadow-hover: 0 15px 35px rgba(0, 0, 0, 0.1);
}



header h1 {
    margin: 0;
    font-size: 1.8rem;
    font-weight: 600;
    letter-spacing: -0.5px;
    color: var(--text-main);
}

header p {
    color: var(--text-muted);
    font-size: 0.9rem;
    margin-top: 0.5rem;
}

/* コントロール */
.controls {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 15px;
    padding: 0 20px;
    flex-wrap: wrap;
    margin-bottom: 40px;
}

/* セレクト */
select {
    padding: 12px 16px;
    font-size: 1rem;
    border: 1px solid #dfe6e9;
    border-radius: 8px;
    background-color: #fff;
    color: var(--text-main);
    cursor: pointer;
    outline: none;
    transition: all 0.2s ease;
    min-width: 200px;
}

select:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(9, 132, 227, 0.1);
}

/* ボタン共通 */
button {
    padding: 12px 24px;
    font-size: 0.95rem;
    font-weight: 600;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s cubic-bezier(0.25, 0.8, 0.25, 1);
}

button#add-clock-btn {
    background-color: var(--text-main);
    color: white;
}

button#add-clock-btn:hover {
    background-color: #000;
    transform: translateY(-2px);
}

button#reset-clock-btn {
    background-color: transparent;
    color: var(--text-muted);
    border: 1px solid #dfe6e9;
}

button#reset-clock-btn:hover {
    background-color: #dfe6e9;
    color: var(--text-main);
}

/* コンテナ */
.clocks-container {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 30px;
    padding: 0 40px 60px 40px;
    max-width: 1400px;
    margin: 0 auto;
}

/* カード */
.clock {
    background: var(--card-bg);
    border-radius: 16px;
    padding: 25px;
    position: relative;
    box-shadow: var(--shadow-soft);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
    border: 1px solid transparent; 
    display: flex;
    flex-direction: column;
    align-items: center;
}

.clock:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-hover);
}

/* 時間シフト時 */
.clock.shifted {
    border-color: var(--accent-warning);
    background: #fffdf9; 
}

.clock.shifted::after {
    content: "TIME SHIFTED";
    position: absolute;
    top: -10px;
    left: 50%;
    transform: translateX(-50%);
    background: var(--accent-warning);
    color: #fff;
    font-size: 0.6rem;
    font-weight: bold;
    padding: 4px 8px;
    border-radius: 12px;
    letter-spacing: 1px;
}

/* 都市名 */
.city-name {
    margin: 0;
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text-main);
    margin-bottom: 5px;
    text-align: center;
}

/* UTCバッジ */
.utc-offset {
    display: inline-block;
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--primary-color);
    background: rgba(9, 132, 227, 0.1);
    padding: 4px 10px;
    border-radius: 20px;
    margin-bottom: 20px;
}

/* 時計表示 */
.digital-clock {
    font-family: 'Roboto Mono', monospace; 
    font-size: 2.5rem;
    font-weight: 500;
    color: var(--text-main);
    letter-spacing: -1px;
    line-height: 1;
    margin-bottom: 5px;
    font-variant-numeric: tabular-nums; 
}

.date-display {
    font-size: 0.9rem;
    color: var(--text-muted);
    margin-bottom: 20px;
}

/* 日時入力エリア */
.datetime-input {
    width: 100%;
    padding: 8px;
    border: 1px solid #f1f2f6;
    border-radius: 6px;
    background: #f8f9fa;
    color: var(--text-muted);
    font-size: 0.8rem;
    text-align: center;
    transition: all 0.2s;
}

.datetime-input:focus {
    background: #fff;
    border-color: var(--primary-color);
    outline: none;
}

/* 削除ボタン */
.remove-btn {
    position: absolute;
    top: 15px;
    right: 15px;
    width: 24px;
    height: 24px;
    padding: 0;
    background: transparent;
    color: #dfe6e9;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.2rem;
    line-height: 1;
    transition: all 0.2s;
}

.remove-btn:hover {
    color: var(--accent-danger);
    background: rgba(255, 118, 117, 0.1);
    transform: rotate(90deg); 
}

/* SP */
@media (max-width: 600px) {
    .controls {
        flex-direction: column;
        width: 100%;
        box-sizing: border-box;
    }
    
    select, button {
        width: 100%;
    }
    
    .clocks-container {
        grid-template-columns: 1fr;
        padding: 0 20px;
    }
}

/* --- 使用法セクション --- */
.usage-section {
    max-width: 1000px;
    margin: 40px auto;
    padding: 0 20px;
    text-align: center;
    color: var(--text-muted);
    font-size: 0.9rem;
}

/* アコーディオンの開閉部分 */
.usage-section details {
    border: 1px solid #eee;
    background: #fff;
    border-radius: 8px;
    overflow: hidden;
    transition: all 0.3s ease;
}

.usage-section details[open] {
    box-shadow: var(--shadow-soft);
    border-color: transparent;
}

.usage-section summary {
    padding: 15px;
    cursor: pointer;
    font-weight: 600;
    list-style: none;
    transition: background-color 0.2s;
    user-select: none;
    background-color: #fcfcfc;
}

.usage-section summary:hover {
    background-color: #f1f2f6;
    color: var(--primary-color);
}

.usage-section summary::-webkit-details-marker {
    display: none;
}

.usage-section summary::after {
    content: "+";
    display: inline-block;
    float: right; /* 右端に寄せる */
    font-weight: bold;
    transition: transform 0.3s;
}

.usage-section details[open] summary::after {
    transform: rotate(45deg);
}

.usage-content {
    text-align: left;
    background: #fff;
    padding: 20px 30px;
    border-top: 1px solid #eee;
    animation: fadeInContent 0.3s ease-out;
}

@keyframes fadeInContent {
    from { opacity: 0; }
    to { opacity: 1; }
}

.usage-content ul {
    padding-left: 20px;
    margin: 0;
}

.usage-content li {
    margin-bottom: 8px;
    line-height: 1.6;
}

.usage-content strong {
    color: var(--text-main);
    display: inline-block;
    min-width: 120px; 
}