* {
    box-sizing: border-box;
}

html, body {
    overflow-x: hidden;
    width: 100%;
}

/* Basic Page Setup */
body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: #f5f5f6;
    margin: 0;
    padding: 0;
    color: #333;
}

.container,
.subchapter-list,
.subchapter-card,
.subchapter-link,
.subchapter-name,
h1,
h2,
p,
a {
    overflow-wrap: anywhere;
    word-break: break-word;
}

/* Header */
.header-container {
    background: transparent;
    color: #1a237e;
    text-align: center;
    padding: 40px 20px 30px;
}

.header-container h1 {
    font-size: 34px;
    margin: 0 0 8px;
    letter-spacing: 0.5px;
}

.header-container .subtitle {
    font-size: 17px;
    color: #555;
    margin: 0 0 16px;
}

.breadcrumb {
    font-size: 14px;
    color: #666;
}

.breadcrumb a {
    color: #1a237e;
    text-decoration: none;
    font-weight: 500;
    transition: color 0.2s;
}

.breadcrumb a:hover {
    color: #3949ab;
}

.breadcrumb span {
    color: #333;
}

/* Container */
.container {
    width: 90%;
    max-width: 900px;
    min-width: 0;
    margin: 40px auto;
    display: flex;
    flex-direction: column;
    align-items: center;
}

/* Subchapter List */
.subchapter-list {
    display: flex;
    flex-direction: column;
    gap: 16px;
    width: 100%;
    align-items: center;
}

/* Subchapter Card */
.subchapter-card {
    width: 90%;
    max-width: 650px;
    background: #fff;
    border-radius: 12px;
    box-shadow: 0 4px 14px rgba(0, 0, 0, 0.08);
    display: flex;
    align-items: stretch;
    overflow: hidden;
    transition: all 0.3s ease;
    animation: slideIn 0.4s ease forwards;
    opacity: 0;
    transform: translateY(15px);
}

@keyframes slideIn {
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.subchapter-card:nth-child(1)  { animation-delay: 0ms; }
.subchapter-card:nth-child(2)  { animation-delay: 60ms; }
.subchapter-card:nth-child(3)  { animation-delay: 120ms; }
.subchapter-card:nth-child(4)  { animation-delay: 180ms; }
.subchapter-card:nth-child(5)  { animation-delay: 240ms; }
.subchapter-card:nth-child(6)  { animation-delay: 300ms; }
.subchapter-card:nth-child(7)  { animation-delay: 360ms; }
.subchapter-card:nth-child(8)  { animation-delay: 420ms; }
.subchapter-card:nth-child(9)  { animation-delay: 480ms; }
.subchapter-card:nth-child(10) { animation-delay: 540ms; }
.subchapter-card:nth-child(11) { animation-delay: 600ms; }
.subchapter-card:nth-child(12) { animation-delay: 660ms; }
.subchapter-card:nth-child(13) { animation-delay: 720ms; }
.subchapter-card:nth-child(14) { animation-delay: 780ms; }
.subchapter-card:nth-child(15) { animation-delay: 840ms; }
.subchapter-card:nth-child(16) { animation-delay: 900ms; }
.subchapter-card:nth-child(17) { animation-delay: 960ms; }

.subchapter-card:hover {
    transform: translateX(6px);
    box-shadow: 0 8px 28px rgba(26, 35, 126, 0.18);
    background: #e8eaf6;
}

/* Card Number */
.card-number {
    background: linear-gradient(135deg, #1a237e, #3949ab);
    color: #fff;
    font-weight: 700;
    font-size: 18px;
    min-width: 50px;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
}

/* Subchapter Link */
.subchapter-link {
    display: flex;
    flex: 1;
    align-items: center;
    padding: 18px 24px;
    text-decoration: none;
    color: #1a237e;
    gap: 12px;
}

.subchapter-name {
    font-weight: 600;
    font-size: 17px;
    flex: 1;
}

/* Empty State */
.empty-state {
    text-align: center;
    padding: 60px 20px;
    color: #999;
    font-size: 18px;
}

/* Navigation Buttons */
.nav-buttons {
    margin: 35px 0;
    display: flex;
    gap: 16px;
    flex-wrap: wrap;
    justify-content: center;
}

.btn {
    display: inline-block;
    padding: 14px 30px;
    border-radius: 10px;
    text-decoration: none;
    font-weight: bold;
    font-size: 16px;
    transition: background-color 0.3s, transform 0.3s;
}

.btn-back {
    background-color: #344a84;
    color: #fff;
}

.btn-back:hover {
    background-color: #46c467;
    transform: translateY(-3px);
}

/* Footer */
.footer {
    margin-top: 50px;
    padding: 30px 20px;
    background: #1a237e;
    color: #fff;
    text-align: center;
    font-size: 16px;
    line-height: 1.6;
}

.footer a {
    color: #fdd835;
    text-decoration: none;
    font-weight: 600;
    margin: 0 8px;
    transition: color 0.2s;
}

.footer a:hover {
    color: #fff;
}

img,
video,
iframe,
table {
    max-width: 100%;
}

/* Responsive */
@media (max-width: 600px) {
    .container {
        width: calc(100% - 16px);
        margin: 20px auto;
    }

    .header-container h1 {
        font-size: 26px;
    }

    .subchapter-card {
        width: 100%;
    }

    .subchapter-link {
        flex-direction: column;
        align-items: flex-start;
        padding: 14px 18px;
        gap: 6px;
    }

    .subchapter-name {
        font-size: 15px;
    }

    .btn {
        width: 100%;
        text-align: center;
    }

    .subchapter-card:hover,
    .btn-back:hover {
        transform: none;
        box-shadow: none;
    }
}