/* Statistical Learning section styles */
header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 20px;
    margin-bottom: 40px;
}

header h1 {
    font-family: 'Chakra Petch', sans-serif;
    font-size: 2.5em;
    color: #ffffff;
    margin: 0;
    text-shadow: 
        2px 2px 0 rgba(0,0,0,0.8),
        3px 3px 4px rgba(0,0,0,0.4);
}

.back-link {
    color: #fff;
    text-decoration: none;
    font-family: 'Space Mono', monospace;
    padding: 10px 20px;
    border: 2px solid #fff;
    border-radius: 5px;
    transition: all 0.3s ease;
}

.back-link:hover {
    background: rgba(255, 255, 255, 0.1);
    transform: translateX(-5px);
}

/* Content styles */
.content {
    max-width: 1000px;
    margin: 0 auto;
    padding: 40px 20px;
}

.intro {
    margin-bottom: 40px;
}

.intro p {
    font-family: 'Space Mono', monospace;
    font-size: 1.1em;
    line-height: 1.6;
    color: rgba(255, 255, 255, 0.9);
}

/* Documents Grid */
.documents-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2em;
}

.document-card {
    border: 2px solid rgba(255, 255, 255, 0.2);
    border-radius: 10px;
    padding: 1.5em;
    transition: all 0.3s ease;
    opacity: 0;
    animation: fadeIn 0.6s ease-out forwards;
}

.document-card:hover {
    border-color: rgba(255, 255, 255, 0.4);
    transform: translateY(-5px);
}

.document-card h2 {
    font-family: 'Chakra Petch', sans-serif;
    font-size: 1.3em;
    color: #ffffff;
    margin: 0 0 1em 0;
    text-shadow: 
        1px 1px 0 rgba(0,0,0,0.8),
        2px 2px 3px rgba(0,0,0,0.4);
}

.document-actions {
    display: flex;
    justify-content: center;
}

.document-actions a {
    font-family: 'Space Mono', monospace;
    font-size: 0.9em;
    color: #fff;
    text-decoration: none;
    padding: 0.5em 1em;
    border: 1px solid rgba(255, 255, 255, 0.4);
    border-radius: 5px;
    transition: all 0.3s ease;
    text-align: center;
    width: 100px;
}

.document-actions a:hover {
    background: rgba(255, 255, 255, 0.1);
    transform: translateY(-2px);
}

/* Animation */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* Stagger animations */
.document-card:nth-child(1) { animation-delay: 0.1s; }
.document-card:nth-child(2) { animation-delay: 0.2s; }
.document-card:nth-child(3) { animation-delay: 0.3s; }
.document-card:nth-child(4) { animation-delay: 0.4s; }

/* Responsive adjustments */
@media (max-width: 768px) {
    header {
        flex-direction: column;
        gap: 20px;
        text-align: center;
    }

    header h1 {
        font-size: 2em;
    }

    .content {
        padding: 20px;
    }

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

    .document-card {
        padding: 1em;
    }
}

/* Book link */
.book-link {
    color: #fff;
    text-decoration: none;
    border-bottom: 1px solid rgba(255, 255, 255, 0.4);
    transition: all 0.3s ease;
}

.book-link:hover {
    border-bottom-color: #fff;
}

.book-link::after {
    content: '↗';
    display: inline-block;
    margin-left: 4px;
    font-size: 0.8em;
    transition: transform 0.2s ease;
}

.book-link:hover::after {
    transform: translate(2px, -2px);
}

/* Pending message */
.pending-message {
    text-align: center;
    margin-top: 3em;
    font-family: 'Space Mono', monospace;
    font-size: 1.1em;
    color: rgba(255, 255, 255, 0.8);
    animation: blink 2s infinite;
}

@keyframes blink {
    0% { opacity: 0.3; }
    50% { opacity: 1; }
    100% { opacity: 0.3; }
}