:root {
    --bg-0: #0e1116;
    --bg-1: #151a21;
    --bg-2: #1d2430;
    --ink-0: #e8eef6;
    --ink-1: #c6d2e3;
    --ink-2: #8fa3bf;
    --accent-0: #4dd6ff;
    --accent-1: #7b8cff;
    --accent-2: #f7b84b;
    --success: #4bd37b;
    --danger: #ff7b7b;
    --card: #141a22;
    --glass: rgba(20, 26, 34, 0.7);
    --border: rgba(140, 160, 190, 0.18);
    --shadow: 0 20px 60px rgba(0, 0, 0, 0.35);
}

* {
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
}

body {
    margin: 0;
    font-family: "Space Grotesk", "Segoe UI", sans-serif;
    color: var(--ink-0);
    background: radial-gradient(1200px 800px at 10% 10%, rgba(77, 214, 255, 0.15), transparent 60%),
        radial-gradient(1200px 900px at 90% 0%, rgba(123, 140, 255, 0.18), transparent 65%),
        var(--bg-0);
}

a {
    color: inherit;
    text-decoration: none;
}

.topbar {
    position: sticky;
    top: 0;
    z-index: 20;
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 18px 28px;
    backdrop-filter: blur(16px);
    background: rgba(14, 17, 22, 0.85);
    border-bottom: 1px solid var(--border);
}

.brand {
    width: 100%;
    display: flex;
    align-items: center;
    gap: 12px;
    font-weight: 700;
    letter-spacing: 0.04em;
    text-transform: uppercase;
}

.brand-badge {
    width: 38px;
    height: 38px;
    border-radius: 12px;
    display: grid;
    place-items: center;
    background: linear-gradient(135deg, var(--accent-0), var(--accent-1));
    color: #0b0e12;
    font-weight: 700;
}

.top-actions {
    width: 100%;
    display: flex;
    align-items: center;
    gap: 16px;
}

.search {
    width: 100%;
    position: relative;
}

.search input {
    width: min(360px, 50vw);
    padding: 12px 14px 12px 38px;
    border-radius: 999px;
    border: 1px solid var(--border);
    background: var(--glass);
    color: var(--ink-0);
    font-size: 0.95rem;
}

.search svg {
    position: absolute;
    width: 20px;
    left: 12px;
    top: 50%;
    transform: translateY(-50%);
    color: var(--ink-2);
    fill: var(--ink-2);
    font-size: 0.85rem;
}

.progress {
    width: 100%;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 10px;
    font-size: 0.9rem;
    color: var(--ink-1);
}

.progress-bar {
    width: 140px;
    height: 6px;
    border-radius: 99px;
    background: rgba(255, 255, 255, 0.08);
    overflow: hidden;
}

.progress-bar span {
    display: block;
    height: 100%;
    width: 0;
    background: linear-gradient(90deg, var(--accent-0), var(--accent-1));
}

.layout {
    display: grid;
    grid-template-columns: 260px minmax(0, 1fr);
    gap: 28px;
    padding: 28px;
}

.sidebar {
    position: sticky;
    top: 90px;
    height: fit-content;
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: 18px;
    padding: 20px;
    box-shadow: var(--shadow);
}

.sidebar h3 {
    margin: 0 0 12px;
    font-size: 0.95rem;
    text-transform: uppercase;
    letter-spacing: 0.12em;
    color: var(--ink-2);
}

.nav-list {
    display: grid;
    gap: 10px;
}

.nav-item {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 10px 12px;
    border-radius: 12px;
    background: transparent;
    border: 1px solid transparent;
    color: var(--ink-1);
    transition: 0.2s ease;
}

.nav-item.active {
    background: rgba(77, 214, 255, 0.08);
    border-color: rgba(77, 214, 255, 0.3);
    color: var(--ink-0);
}

.nav-item span {
    font-size: 0.8rem;
    color: var(--ink-2);
}

.hero {
    display: grid;
    gap: 20px;
    margin-bottom: 28px;
    background: linear-gradient(135deg, rgba(77, 214, 255, 0.15), rgba(123, 140, 255, 0.15));
    border-radius: 24px;
    padding: 28px;
    border: 1px solid var(--border);
    box-shadow: var(--shadow);
}

.hero h1 {
    margin: 0;
    font-size: clamp(2rem, 3vw, 3rem);
}

.hero p {
    margin: 0;
    color: var(--ink-1);
    max-width: 700px;
}

.hero-actions {
    display: flex;
    flex-wrap: wrap;
    gap: 12px;
}

.button {
    padding: 12px 18px;
    border-radius: 12px;
    border: 1px solid transparent;
    font-weight: 600;
    cursor: pointer;
    transition: 0.2s ease;
    font-family: inherit;
}

.button.primary {
    background: linear-gradient(135deg, var(--accent-0), var(--accent-1));
    color: #0b0e12;
}

.button.ghost {
    background: transparent;
    border-color: var(--border);
    color: var(--ink-0);
}

.lesson {
    margin-bottom: 28px;
    padding: 24px;
    border-radius: 20px;
    background: var(--card);
    border: 1px solid var(--border);
    box-shadow: var(--shadow);
}

.lesson-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    gap: 20px;
    flex-wrap: wrap;
}

.lesson-header h2 {
    margin: 0 0 6px;
    font-size: 1.8rem;
}

.lesson-meta {
    display: flex;
    gap: 12px;
    flex-wrap: wrap;
    color: var(--ink-2);
    font-size: 0.9rem;
}

.chip {
    padding: 6px 12px;
    border-radius: 999px;
    background: rgba(255, 255, 255, 0.06);
    border: 1px solid var(--border);
}

.lesson-grid {
    margin-top: 20px;
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: 18px;
}

.card {
    padding: 16px;
    border-radius: 16px;
    border: 1px solid var(--border);
    background: rgba(12, 15, 20, 0.7);
}

.card h4 {
    margin: 0 0 8px;
    font-size: 1rem;
}

.code-block {
    margin-top: 12px;
    position: relative;
    border-radius: 14px;
    padding: 14px;
    background: #0b0f14;
    border: 1px solid rgba(255, 255, 255, 0.1);
    font-family: "JetBrains Mono", monospace;
    font-size: 0.85rem;
    overflow: auto;
}

.code-block button {
    position: absolute;
    top: 12px;
    right: 12px;
    padding: 6px 10px;
    font-size: 0.75rem;
    border-radius: 8px;
    border: 1px solid var(--border);
    background: rgba(255, 255, 255, 0.05);
    color: var(--ink-1);
    cursor: pointer;
}

.step-list {
    display: grid;
    gap: 12px;
    margin: 12px 0 0;
    padding: 0;
    list-style: none;
}

.step-list li {
    display: flex;
    gap: 10px;
    align-items: flex-start;
    color: var(--ink-1);
}

.step-list span {
    width: 26px;
    height: 26px;
    border-radius: 8px;
    display: grid;
    place-items: center;
    background: rgba(77, 214, 255, 0.15);
    color: var(--accent-0);
    font-weight: 700;
}

.quiz {
    display: grid;
    gap: 10px;
}

.quiz input {
    width: 100%;
    padding: 10px 12px;
    border-radius: 10px;
    border: 1px solid var(--border);
    background: rgba(255, 255, 255, 0.05);
    color: var(--ink-0);
}

.quiz-result {
    font-size: 0.85rem;
    color: var(--ink-2);
}

.lesson-footer {
    margin-top: 18px;
    display: flex;
    flex-wrap: wrap;
    gap: 12px;
    align-items: center;
}

.mark {
    padding: 10px 16px;
    border-radius: 12px;
    border: 1px solid var(--border);
    background: rgba(255, 255, 255, 0.04);
    color: var(--ink-0);
    cursor: pointer;
    font-weight: 600;
}

.mark.done {
    background: rgba(75, 211, 123, 0.2);
    border-color: rgba(75, 211, 123, 0.5);
    color: var(--success);
}

/* .footer {
    padding: 30px 28px 50px;
    color: var(--ink-2);
    text-align: center;
} */

.return {
    margin-top: 12px;
    display: inline-flex;
    gap: 8px;
    align-items: center;
    padding: 10px 14px;
    border-radius: 999px;
    border: 1px solid var(--border);
    background: rgba(255, 255, 255, 0.05);
}

@media (max-width: 980px) {
    .layout {
        grid-template-columns: 1fr;
    }

    .sidebar {
        position: relative;
        top: 0;
    }

    .topbar {
        flex-direction: column;
        align-items: flex-start;
        gap: 14px;
    }

    .search input {
        width: min(100%, 520px);
    }

    .top-actions {
        justify-content: space-around;
    }
}