:root {
    --bg-main: #0d1117;
    --bg-card: #111827;
    --bg-panel: #020617;
    --accent: #38bdf8;
    --accent-soft: #0ea5e9;
    --text-main: #e5e7eb;
    --text-muted: #9ca3af;
    --success: #22c55e;
    --border-soft: #1f2937;
    --shadow-soft: 0 18px 40px rgba(15, 23, 42, 0.7);
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    background: radial-gradient(
        circle at top,
        #020617 0,
        #020617 40%,
        #020617 100%
    );
    color: var(--text-main);
    font-family:
        system-ui,
        -apple-system,
        BlinkMacSystemFont,
        "Segoe UI",
        sans-serif;
    display: flex;
    justify-content: center;
    align-items: stretch;
    min-height: 100vh;
}

.page {
    max-width: 1100px;
    width: 100%;
    padding: 24px 16px;
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.header {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.header-left h1 {
    margin: 0;
    font-size: 22px;
    letter-spacing: 0.02em;
}

.header-left p {
    margin: 4px 0 0;
    font-size: 13px;
    color: var(--text-muted);
}

.header-badge {
    padding: 6px 10px;
    border-radius: 999px;
    background: rgba(56, 189, 248, 0.12);
    border: 1px solid rgba(56, 189, 248, 0.4);
    font-size: 12px;
    color: var(--accent-soft);
}

.layout {
    display: grid;
    grid-template-columns: minmax(0, 1.5fr) minmax(0, 2.5fr);
    gap: 14px;
}

@media (max-width: 900px) {
    .layout {
        grid-template-columns: minmax(0, 1fr);
    }
}

.card {
    border-radius: 16px;
    background: linear-gradient(135deg, #020617 0, #020617 10%, #111827 100%);
    border: 1px solid var(--border-soft);
    box-shadow: var(--shadow-soft);
    overflow: hidden;
    position: relative;
}

.card-header {
    padding: 10px 14px;
    border-bottom: 1px solid #1f2937;
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: radial-gradient(
        circle at left,
        rgba(56, 189, 248, 0.08),
        transparent 55%
    );
}

.card-header-left {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 13px;
    color: var(--text-muted);
}

.card-header-left-dot {
    width: 10px;
    height: 10px;
    border-radius: 999px;
    background: #22c55e;
    box-shadow: 0 0 0 4px rgba(34, 197, 94, 0.25);
}

.card-header-right {
    font-size: 11px;
    color: var(--accent);
}

#terminal-container {
    height: 420px;
    padding: 12px 14px;
}

.xterm {
    padding: 2px 4px;
    border-radius: 10px;
    background: #020617;
    border: 1px solid #1f2937;
}

/* Lesson panel */
.lesson-card {
    border-radius: 16px;
    background: var(--bg-card);
    border: 1px solid var(--border-soft);
    box-shadow: var(--shadow-soft);
    padding: 16px 16px 18px;
    display: flex;
    flex-direction: column;
    gap: 10px;
}

.lesson-title-row {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 8px;
}

#lesson-title {
    font-size: 16px;
    font-weight: 600;
}

#lesson-badge {
    font-size: 11px;
    padding: 3px 8px;
    border-radius: 999px;
    background: rgba(34, 197, 94, 0.1);
    color: var(--success);
    border: 1px solid rgba(34, 197, 94, 0.4);
}

#lesson-description {
    font-size: 13px;
    color: var(--text-muted);
    line-height: 1.5;
    white-space: pre-line;
}

.lesson-meta {
    display: flex;
    flex-wrap: wrap;
    gap: 6px;
    font-size: 11px;
    color: var(--text-muted);
}

.meta-pill {
    padding: 3px 7px;
    border-radius: 999px;
    border: 1px solid #1f2937;
    background: #020617;
}

#lesson-status {
    margin-top: 4px;
    font-size: 12px;
    color: var(--success);
}

.lesson-footer {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-top: 6px;
    font-size: 11px;
    color: var(--text-muted);
}

.hint {
    font-style: italic;
}

.progress-bar {
    position: relative;
    height: 5px;
    border-radius: 999px;
    background: #020617;
    overflow: hidden;
    margin-top: 6px;
}

.progress-bar-inner {
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    width: 0%;
    background: linear-gradient(90deg, #22c55e, #38bdf8);
    transition: width 0.25s ease-out;
}

/* Lesson navigation */
.lesson-navigation {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-top: 12px;
    padding-top: 12px;
    border-top: 1px solid var(--border-soft);
}

.nav-btn {
    display: inline-flex;
    align-items: center;
    gap: 4px;
    background: #020617;
    border: 1px solid var(--border-soft);
    color: var(--text-main);
    padding: 6px 12px;
    border-radius: 8px;
    font-size: 12px;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s ease;
    user-select: none;
}

.nav-btn:hover:not(:disabled) {
    background: rgba(56, 189, 248, 0.08);
    border-color: var(--accent);
    color: var(--accent);
}

.nav-btn:disabled {
    opacity: 0.3;
    cursor: not-allowed;
}

.nav-btn svg {
    transition: transform 0.2s ease;
}

#prev-lesson-btn:hover:not(:disabled) svg {
    transform: translateX(-2px);
}

#next-lesson-btn:hover:not(:disabled) svg {
    transform: translateX(2px);
}