:root {
    --bg: #0e1726;
    --card: #1b2c47;
    --card-2: #213655;
    --line: #2c456e;
    --text: #e8eef7;
    --muted: #9db0cc;
    --accent: #4ea1ff;
    --accent-2: #3ad0a4;
    --warn: #ffb454;
    --danger: #ff6b6b;
    --ok: #3ad0a4;
    --shadow: 0 10px 30px rgba(0, 0, 0, 0.35);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }

body {
    margin: 0;
    font-family: "Segoe UI", "Helvetica Neue", Arial, sans-serif;
    background: radial-gradient(1200px 600px at 80% -10%, #1c3357 0%, var(--bg) 55%);
    color: var(--text);
    line-height: 1.65;
    font-size: 17px;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

.wrap { max-width: 900px; margin: 0 auto; padding: 32px 20px 96px; }

.topbar {
    position: sticky; top: 0; z-index: 20;
    backdrop-filter: blur(10px);
    background: rgba(14, 23, 38, 0.82);
    border-bottom: 1px solid var(--line);
}

.topbar-inner {
    max-width: 900px; margin: 0 auto; padding: 12px 20px;
    display: flex; align-items: center; justify-content: space-between; gap: 16px;
}

.brand { font-weight: 700; display: flex; align-items: center; gap: 10px; }
.brand .dot {
    width: 10px; height: 10px; border-radius: 50%;
    background: var(--accent-2); box-shadow: 0 0 12px var(--accent-2);
}

.topnav a { color: var(--muted); margin-left: 16px; font-size: 15px; }
.topnav a:hover { color: var(--text); text-decoration: none; }

.kicker {
    color: var(--accent-2); font-weight: 600;
    letter-spacing: 1.5px; font-size: 13px; text-transform: uppercase;
}

.hero {
    background: linear-gradient(160deg, var(--card) 0%, var(--card-2) 100%);
    border: 1px solid var(--line); border-radius: 18px;
    padding: 34px 30px; box-shadow: var(--shadow); margin-bottom: 28px;
}

.hero h1 { margin: 8px 0 10px; font-size: 32px; line-height: 1.2; }
.hero p { color: var(--muted); margin: 0; max-width: 680px; }

h1 { margin-top: 6px; font-size: 30px; line-height: 1.25; }
h2 { margin-top: 42px; font-size: 24px; border-left: 4px solid var(--accent); padding-left: 12px; }
h3 { margin-top: 28px; font-size: 19px; color: #d6e4ff; }
h4 { margin: 0 0 12px; font-size: 18px; }

p { margin: 12px 0; }
ul, ol { padding-left: 22px; }
li { margin: 6px 0; }

.lo {
    display: inline-block;
    font-size: 12px; font-weight: 700; letter-spacing: 0.4px;
    color: var(--accent); background: rgba(78, 161, 255, 0.12);
    border: 1px solid rgba(78, 161, 255, 0.35);
    border-radius: 6px; padding: 2px 8px; margin-right: 6px;
    font-family: "JetBrains Mono", Consolas, monospace;
}

.card {
    background: var(--card); border: 1px solid var(--line);
    border-radius: 14px; padding: 20px 22px; margin: 20px 0;
    box-shadow: var(--shadow);
}

.note {
    border-left: 4px solid var(--accent);
    background: rgba(78, 161, 255, 0.08);
    border-radius: 10px; padding: 14px 18px; margin: 20px 0;
}

.note.warn { border-left-color: var(--warn); background: rgba(255, 180, 84, 0.09); }
.note.exam { border-left-color: var(--accent-2); background: rgba(58, 208, 164, 0.09); }
.note .label {
    font-weight: 700; text-transform: uppercase; letter-spacing: 0.8px;
    font-size: 12px; display: block; margin-bottom: 4px;
}
.note.exam .label { color: var(--accent-2); }
.note.warn .label { color: var(--warn); }
.note .label.info { color: var(--accent); }

table { width: 100%; border-collapse: collapse; margin: 18px 0; font-size: 15px; }
th, td { border: 1px solid var(--line); padding: 10px 12px; text-align: left; vertical-align: top; }
th { background: var(--card-2); color: #d6e4ff; }
tr:nth-child(even) td { background: rgba(255, 255, 255, 0.02); }

.formula {
    background: #0b1220; border: 1px dashed var(--line); border-radius: 10px;
    padding: 14px 18px; margin: 16px 0;
    font-family: "JetBrains Mono", Consolas, monospace; color: #cfe3ff;
}

.cards-grid {
    display: grid; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: 16px; margin: 24px 0;
}

.lesson-card {
    display: block; background: var(--card); border: 1px solid var(--line);
    border-radius: 14px; padding: 18px 20px;
    transition: transform 0.15s ease, border-color 0.15s ease;
}
.lesson-card:hover { transform: translateY(-3px); border-color: var(--accent); text-decoration: none; }
.lesson-card .num { color: var(--accent-2); font-weight: 700; font-size: 13px; letter-spacing: 1px; }
.lesson-card .title { display: block; color: var(--text); font-size: 17px; font-weight: 600; margin: 6px 0 4px; }
.lesson-card .desc { color: var(--muted); font-size: 14px; }
.lesson-card .syll { display: block; margin-top: 8px; font-size: 12px; color: var(--accent); font-family: "JetBrains Mono", Consolas, monospace; }

.pager {
    display: flex; justify-content: space-between; gap: 12px;
    margin-top: 48px; padding-top: 20px; border-top: 1px solid var(--line);
}
.pager a {
    background: var(--card); border: 1px solid var(--line); border-radius: 10px;
    padding: 12px 18px; color: var(--text); max-width: 48%;
}
.pager a:hover { border-color: var(--accent); text-decoration: none; }
.pager .dir {
    display: block; color: var(--muted); font-size: 12px;
    text-transform: uppercase; letter-spacing: 1px;
}

.quiz {
    background: linear-gradient(160deg, #182a49 0%, #1d3358 100%);
    border: 1px solid var(--line); border-radius: 16px;
    padding: 22px 24px; margin: 28px 0; box-shadow: var(--shadow);
}
.quiz-head { display: flex; align-items: center; gap: 10px; margin-bottom: 6px; }
.quiz-head .badge {
    background: var(--accent-2); color: #06231a; font-weight: 700;
    font-size: 12px; padding: 3px 10px; border-radius: 999px;
    text-transform: uppercase; letter-spacing: 0.6px;
}
.quiz-head h4 { margin: 0; }
.quiz .intro { color: var(--muted); font-size: 14px; margin: 0 0 10px; }
.question { margin: 18px 0; padding-top: 14px; border-top: 1px solid rgba(255, 255, 255, 0.06); }
.question:first-of-type { border-top: none; }
.q-text { font-weight: 600; margin: 0 0 10px; }
.options { list-style: none; padding: 0; margin: 0; }
.options li {
    border: 1px solid var(--line); border-radius: 10px; padding: 10px 14px;
    margin: 8px 0; cursor: pointer; background: rgba(255, 255, 255, 0.02);
}
.options li:hover { border-color: var(--accent); }
.options li.selected { border-color: var(--accent); background: rgba(78, 161, 255, 0.14); }
.options li.correct { border-color: var(--ok); background: rgba(58, 208, 164, 0.16); }
.options li.wrong { border-color: var(--danger); background: rgba(255, 107, 107, 0.14); }
.options li .key { display: inline-block; width: 22px; font-weight: 700; color: var(--muted); }
.explanation {
    display: none; margin: 10px 0 0; padding: 10px 14px; border-radius: 10px;
    background: rgba(58, 208, 164, 0.08); border-left: 3px solid var(--accent-2);
    font-size: 15px; color: #d7f5ec;
}
.explanation.show { display: block; }
.quiz-actions { display: flex; align-items: center; gap: 14px; margin-top: 18px; }
.btn {
    background: var(--accent); color: #06182e; border: none; border-radius: 10px;
    padding: 11px 22px; font-weight: 700; font-size: 15px; cursor: pointer;
}
.btn:hover { filter: brightness(1.08); }
.btn.secondary { background: transparent; color: var(--text); border: 1px solid var(--line); }
.result { font-weight: 700; }
.result.pass { color: var(--ok); }
.result.fail { color: var(--warn); }

footer { color: var(--muted); font-size: 14px; text-align: center; padding: 30px 20px 10px; }

@media (max-width: 600px) {
    .hero h1, h1 { font-size: 24px; }
    body { font-size: 16px; }
}