body {
    font-family: 'Helvetica Neue', Arial, sans-serif;
    background-color: #f5f7fa;
    color: #333;
    margin: 0;
    padding: 20px;
}

.container {
    max-width: 900px;
    margin: 0 auto;
    background: #fff;
    padding: 30px;
    border-radius: 8px;
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
}

h1 {
    text-align: center;
    color: #2c3e50;
    margin-bottom: 30px;
}

h2 {
    border-left: 5px solid #3498db;
    padding-left: 10px;
    color: #2c3e50;
    font-size: 1.2rem;
    margin-top: 20px;
}

.instruction {
    font-size: 0.9rem;
    color: #7f8c8d;
    margin-bottom: 15px;
}

/* 設定セクション */
.student-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(130px, 1fr));
    gap: 10px;
    max-height: 250px;
    overflow-y: auto;
    border: 1px solid #e2e8f0;
    padding: 15px;
    border-radius: 6px;
    background: #f8fafc;
}

.student-item {
    display: flex;
    align-items: center;
    gap: 5px;
    font-size: 0.9rem;
    background: white;
    padding: 5px;
    border-radius: 4px;
    border: 1px solid #cbd5e1;
}

.gender-btn {
    border: none;
    padding: 2px 6px;
    border-radius: 3px;
    cursor: pointer;
    font-size: 0.8rem;
    font-weight: bold;
}

.gender-btn.male {
    background-color: #e0f2fe;
    color: #0284c7;
}

.gender-btn.female {
    background-color: #fce7f3;
    color: #db2777;
}

.student-item.disabled {
    opacity: 0.4;
    background-color: #f1f5f9;
}

/* 座席セクション */
.pattern-selector {
    margin-bottom: 15px;
}

.pattern-selector select {
    padding: 6px 12px;
    border-radius: 4px;
    border: 1px solid #cbd5e1;
}

.seat-grid {
    display: grid;
    grid-template-columns: repeat(6, 1fr);
    gap: 12px;
    margin: 20px auto;
    max-width: 600px;
}

.seat {
    aspect-ratio: 1 / 1;
    background-color: #f1f5f9;
    border: 2px dashed #cbd5e1;
    border-radius: 6px;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    transition: all 0.2s;
    font-weight: bold;
}

.seat:hover {
    background-color: #e2e8f0;
}

.seat.empty-seat {
    background-color: #334155;
    border-color: #334155;
    color: white;
}

.seat.empty-seat::after {
    content: "空席";
    font-size: 0.9rem;
}

.seat.assigned {
    border-style: solid;
}

.seat.assigned.m {
    background-color: #bae6fd;
    border-color: #0284c7;
    color: #0369a1;
}

.seat.assigned.f {
    background-color: #fbcfe8;
    border-color: #db2777;
    color: #be185d;
}

.seat-num {
    font-size: 1.2rem;
}

.seat-gender {
    font-size: 0.7rem;
    margin-top: 4px;
    padding: 2px 6px;
    background: rgba(255,255,255,0.5);
    border-radius: 10px;
}

/* ボタン */
.action-section {
    text-align: center;
    margin-top: 30px;
}

#shuffle-btn {
    background-color: #10b981;
    color: white;
    border: none;
    padding: 12px 40px;
    font-size: 1.1rem;
    font-weight: bold;
    border-radius: 6px;
    cursor: pointer;
    box-shadow: 0 4px 6px rgba(16, 185, 129, 0.2);
    transition: background 0.2s;
}

#shuffle-btn:hover {
    background-color: #059669;
}