:root {
            --bg: #070b16;
            --card: rgba(255, 255, 255, 0.03);
            --border: rgba(255, 255, 255, 0.08);
            --accent: #10b981;
        }
        body {
            background-color: var(--bg);
            background-image:
                radial-gradient(circle at 10% 10%, rgba(16, 185, 129, 0.08) 0%, transparent 40%),
                radial-gradient(circle at 90% 80%, rgba(6, 182, 212, 0.05) 0%, transparent 40%),
                radial-gradient(circle at 50% 50%, rgba(251, 191, 36, 0.03) 0%, transparent 50%);
            background-attachment: fixed;
        }
        .glass {
            background: var(--card);
            backdrop-filter: blur(12px);
            -webkit-backdrop-filter: blur(12px);
            border: 1px solid var(--border);
        }
        .shimmer-text {
            background: linear-gradient(90deg, #f8fafc 0%, #10b981 40%, #fbbf24 60%, #10b981 80%, #f8fafc 100%);
            background-size: 200% auto;
            -webkit-background-clip: text;
            background-clip: text;
            -webkit-text-fill-color: transparent;
            animation: shimmer 6s linear infinite;
        }
        @keyframes shimmer {
            to {
                background-position: 200% center;
            }
        }
        .custom-scrollbar::-webkit-scrollbar {
            width: 6px;
            height: 6px;
        }
        .custom-scrollbar::-webkit-scrollbar-track {
            background: transparent;
        }
        .custom-scrollbar::-webkit-scrollbar-thumb {
            background: rgba(255, 255, 255, 0.1);
            border-radius: 4px;
        }
        .custom-scrollbar::-webkit-scrollbar-thumb:hover {
            background: rgba(255, 255, 255, 0.2);
        }
        .tab-btn.active {
            border-color: var(--accent);
            color: #fff;
            background: rgba(16, 185, 129, 0.1);
        }
        .video-wrapper iframe {
            width: 100%;
            height: 100%;
            position: absolute;
            top: 0;
            left: 0;
            border: 0;
        }
.video-wrapper video {
    width: 100%;
    height: 100%;
    position: absolute;
    inset: 0;
    display: block;
    object-fit: contain;
    background: #0a0f1e;
}
        .video-wrapper {
            position: relative;
            padding-bottom: 56.25%;
            height: 0;
            overflow: hidden;
            background: #0a0f1e;
        }
    
body.course-body{ color:#cbd5e1; min-height:100vh; -webkit-font-smoothing:antialiased; }
body.course-body ::selection{ background:rgba(16,185,129,.3); color:#6ee7b7; }

.presentation-intro {
    width: 100%;
    max-width: 68rem;
    margin-inline: auto;
    padding-top: 0.25rem;
}
.introduction-media-grid {
    display: grid;
    grid-template-columns: minmax(11rem, 0.36fr) minmax(0, 1fr) minmax(11rem, 0.36fr);
    align-items: start;
    gap: 1.25rem;
}
.introduction-video {
    width: 100%;
    max-width: 15rem;
    aspect-ratio: 9 / 16;
    overflow: hidden;
    border: 1px solid var(--border);
    border-radius: 16px;
    background: #0a0f1e;
    box-shadow: 0 24px 70px rgba(0,0,0,.35);
}
.introduction-video:first-child { justify-self: end; }
.introduction-video:last-child { justify-self: start; }
.introduction-video video {
    width: 100%;
    height: 100%;
    display: block;
    object-fit: cover;
}
.presentation-column { min-width: 0; }
.presentation-stage {
    position: relative;
    aspect-ratio: 16 / 9;
    overflow: hidden;
    border: 1px solid var(--border);
    border-radius: 16px;
    background: #f5f1e8;
    box-shadow: 0 24px 70px rgba(0,0,0,.35);
}
.presentation-slide {
    position: absolute;
    inset: 0;
    opacity: 0;
    visibility: hidden;
    transition: opacity .35s ease;
}
.presentation-slide.is-active {
    opacity: 1;
    visibility: visible;
}
.presentation-slide img {
    width: 100%;
    height: 100%;
    display: block;
    object-fit: contain;
}
.presentation-arrow {
    position: absolute;
    z-index: 2;
    top: 50%;
    width: 44px;
    height: 44px;
    display: grid;
    place-items: center;
    border: 1px solid rgba(255,255,255,.22);
    border-radius: 50%;
    color: #fff;
    background: rgba(7,11,22,.78);
    transform: translateY(-50%);
    transition: background .2s ease, transform .2s ease;
}
.presentation-arrow:hover { background: rgba(16,185,129,.92); transform: translateY(-50%) scale(1.05); }
.presentation-arrow-prev { left: 1rem; }
.presentation-arrow-next { right: 1rem; }
.presentation-arrow svg { width: 24px; height: 24px; fill: none; stroke: currentColor; stroke-width: 2; }
.presentation-count {
    position: absolute;
    z-index: 2;
    right: 1rem;
    bottom: 1rem;
    min-width: 54px;
    padding: .4rem .65rem;
    border-radius: 999px;
    color: #fff;
    background: rgba(7,11,22,.78);
    font: 600 12px/1 "Plus Jakarta Sans", sans-serif;
    text-align: center;
}
.presentation-controls { display: flex; justify-content: center; padding-top: .75rem; }
.presentation-dots { display: flex; flex-wrap: wrap; justify-content: center; gap: .55rem; }
.presentation-dot {
    width: 8px;
    height: 8px;
    padding: 0;
    border: 0;
    border-radius: 50%;
    background: rgba(255,255,255,.22);
    transition: width .2s ease, background .2s ease;
}
.presentation-dot.is-active { width: 24px; border-radius: 999px; background: var(--accent); }
@media (max-width: 640px) {
    .introduction-media-grid { grid-template-columns: 1fr; gap: 1rem; }
    .introduction-video { width: min(72vw, 15rem); justify-self: center; }
    .introduction-video:first-child, .introduction-video:last-child { justify-self: center; }
    .presentation-stage { border-radius: 10px; }
    .presentation-arrow { width: 36px; height: 36px; }
    .presentation-arrow-prev { left: .5rem; }
    .presentation-arrow-next { right: .5rem; }
    .presentation-count { right: .5rem; bottom: .5rem; }
}
@media (prefers-reduced-motion: reduce) {
    .presentation-slide, .presentation-arrow, .presentation-dot { transition: none; }
}