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

:root {
    --primary-color: #000000;
    --primary-dark: #1a1a1a;
    --secondary-color: #333333;
    --text-color: #000000;
    --text-light: #4a4a4a;
    --bg-color: #ffffff;
    --bg-light: #f5f5f5;
    --border-color: #d0d0d0;
    --shadow: 0 1px 3px 0 rgba(0, 0, 0, 0.1), 0 1px 2px 0 rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --radius: 8px;
    --radius-lg: 12px;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--bg-light);
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* Header */
header {
    background: #000000;
    color: white;
    padding: 60px 0;
    box-shadow: var(--shadow-lg);
}

header h1 {
    font-size: 2.5rem;
    margin-bottom: 20px;
    font-weight: 700;
}

.subtitle {
    font-size: 1.2rem;
    margin-bottom: 30px;
    opacity: 0.95;
    line-height: 1.8;
}


/* Module Index */
.module-index {
    background: white;
    border-radius: var(--radius-lg);
    padding: 40px;
    margin-bottom: 40px;
    box-shadow: var(--shadow);
}

.module-index h2 {
    font-size: 2rem;
    color: var(--text-color);
    margin-bottom: 15px;
    text-align: center;
}

.index-intro {
    text-align: center;
    font-size: 1.1rem;
    color: var(--text-light);
    margin-bottom: 30px;
}

.index-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 20px;
    margin-top: 30px;
}

.index-card {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 30px 20px;
    background: var(--bg-light);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-lg);
    text-decoration: none;
    color: var(--text-color);
    transition: all 0.3s ease;
    text-align: center;
}

.index-card:hover {
    background: var(--text-color);
    color: white;
    transform: translateY(-5px);
    box-shadow: var(--shadow-lg);
    border-color: var(--text-color);
}

.index-card i {
    margin-bottom: 15px;
    color: inherit;
}

.index-card h3 {
    font-size: 1.3rem;
    margin-bottom: 10px;
    color: inherit;
}

.index-card p {
    font-size: 0.95rem;
    color: inherit;
    opacity: 0.9;
}

/* Module Navigation */
.module-navigation {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-top: 40px;
    padding-top: 30px;
    border-top: 2px solid var(--border-color);
    gap: 15px;
    flex-wrap: wrap;
}

.nav-button {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 15px 25px;
    background: var(--text-color);
    color: white;
    text-decoration: none;
    border-radius: var(--radius);
    font-weight: 600;
    transition: all 0.3s ease;
    flex: 1;
    justify-content: center;
    max-width: 300px;
}

.nav-button:hover {
    background: var(--primary-dark);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.nav-button.prev {
    margin-right: auto;
    margin-left: 0;
}

.nav-button.next {
    margin-left: auto;
    margin-right: 0;
}

.nav-button.index {
    background: var(--bg-light);
    color: var(--text-color);
    border: 2px solid var(--border-color);
    margin: 0 auto;
    max-width: 200px;
}

.nav-button.index:hover {
    background: var(--text-color);
    color: white;
    border-color: var(--text-color);
}

.nav-button i {
    width: 20px;
    height: 20px;
    stroke: currentColor;
}

/* Main Content */
main {
    padding: 40px 0;
}

.module {
    background: white;
    border-radius: var(--radius-lg);
    padding: 40px;
    margin-bottom: 40px;
    box-shadow: var(--shadow);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.module:hover {
    box-shadow: var(--shadow-lg);
    transform: translateY(-2px);
}

.module-header {
    margin-bottom: 30px;
    padding-bottom: 20px;
    border-bottom: 2px solid var(--border-color);
}

.module-header h2 {
    font-size: 2rem;
    color: var(--text-color);
    margin-bottom: 20px;
    display: flex;
    align-items: center;
}

.video-container {
    margin-top: 20px;
}

.video-label {
    font-size: 1.1rem;
    font-weight: 600;
    margin-bottom: 15px;
    color: var(--text-color);
}

.video-container iframe {
    width: 100%;
    height: 500px;
    border: none;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    margin-bottom: 15px;
}

.video-container iframe:not(:last-child) {
    margin-bottom: 20px;
}

.intro {
    font-size: 1.1rem;
    color: var(--text-light);
    margin-bottom: 30px;
    padding: 20px;
    background: var(--bg-light);
    border-left: 4px solid var(--text-color);
    border-radius: var(--radius);
}

.content h3 {
    font-size: 1.5rem;
    color: var(--text-color);
    margin-top: 30px;
    margin-bottom: 15px;
    padding-bottom: 10px;
    border-bottom: 1px solid var(--border-color);
}

.content h3:first-child {
    margin-top: 0;
}

.content p {
    margin-bottom: 15px;
    line-height: 1.8;
    color: var(--text-color);
}

.content ul {
    margin-left: 20px;
    margin-bottom: 20px;
    line-height: 1.8;
}

.content ul li {
    margin-bottom: 10px;
    color: var(--text-color);
}

.content ul ul {
    margin-top: 10px;
    margin-left: 30px;
    list-style-type: circle;
}

.content strong {
    color: var(--text-color);
    font-weight: 600;
}

.conclusion {
    background: #000000;
    color: white;
}

.conclusion h2 {
    color: white;
    border-bottom: 2px solid rgba(255, 255, 255, 0.3);
}

.conclusion p {
    color: rgba(255, 255, 255, 0.95);
    font-size: 1.1rem;
}

/* Footer */
footer {
    background: var(--text-color);
    color: white;
    padding: 30px 0;
    text-align: center;
    margin-top: 60px;
}

footer p {
    opacity: 0.8;
}

/* Responsive Design */
@media (max-width: 768px) {
    header h1 {
        font-size: 2rem;
    }

    .subtitle {
        font-size: 1rem;
    }

    .index-grid {
        grid-template-columns: 1fr;
    }

    .index-card {
        padding: 25px 15px;
    }

    .module-navigation {
        flex-direction: column;
    }

    .nav-button {
        max-width: 100%;
        width: 100%;
    }

    .module {
        padding: 25px;
        margin-bottom: 30px;
    }

    .module-header h2 {
        font-size: 1.5rem;
    }

    .video-container iframe {
        height: 300px;
    }

    .content h3 {
        font-size: 1.3rem;
    }
}

@media (max-width: 480px) {
    header {
        padding: 40px 0;
    }

    header h1 {
        font-size: 1.5rem;
    }

    .subtitle {
        font-size: 0.95rem;
    }

    .module {
        padding: 20px;
    }

    .video-container iframe {
        height: 250px;
    }
}

/* Module Divider */
.module-divider {
    text-align: center;
    padding: 30px 0;
    margin: 20px 0;
}

/* Smooth Scroll */
html {
    scroll-behavior: smooth;
}

/* Scrollbar Styling */
::-webkit-scrollbar {
    width: 10px;
}

::-webkit-scrollbar-track {
    background: var(--bg-light);
}

::-webkit-scrollbar-thumb {
    background: var(--text-color);
    border-radius: 5px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--primary-dark);
}