body {
    font-family: 'Sarabun', sans-serif;
    margin: 0;
    background-color: #f4f7f6;
    color: #333;
}

header, main {
    max-width: 95%;
    margin: 0 auto;
    padding: 20px;
    text-align: center;
}

header {
    background-color: #005a8d;
    color: white;
    border-radius: 0 0 15px 15px;
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}

h1 { margin: 0; }

/* --- Tab Menu Styles --- */
.tab-container {
    display: flex;
    justify-content: center;
    margin-top: 20px;
    border-bottom: 2px solid #ddd;
}

.tab-link {
    font-family: 'Sarabun', sans-serif;
    font-size: 18px;
    font-weight: bold;
    padding: 10px 30px;
    border: none;
    background-color: transparent;
    cursor: pointer;
    color: #666;
    border-bottom: 3px solid transparent;
    transition: all 0.2s ease;
}

.tab-link:hover {
    color: #005a8d;
}

.tab-link.active {
    color: #0077b6;
    border-bottom-color: #0077b6;
}

/* --- Tab Content Styles --- */
.tab-content {
    display: none; /* ซ่อนเนื้อหาทั้งหมดไว้ก่อน */
}

.tab-content.active {
    display: block; /* แสดงเฉพาะเนื้อหาของแท็บที่ถูกเลือก */
}

.sheet-container {
    border: 1px solid #ddd;
    border-radius: 15px;
    overflow: hidden;
    margin-top: 20px;
    box-shadow: 0 4px 15px rgba(0,0,0,0.1);
    height: 80vh;
}

.sheet-container iframe {
    border: none;
    width: 100%;
    height: 100%;
}

.back-link {
    display: inline-block;
    margin-top: 20px;
    padding: 10px 20px;
    background-color: #6c757d;
    color: white;
    text-decoration: none;
    border-radius: 8px;
    transition: background-color 0.2s;
}

.back-link:hover {
    background-color: #5a6268;
}