:root {
  --bg: #f4f7fb;
  --card: #ffffff;
  --ink: #1f2a44;
  --muted: #6b7a99;
  --brand: #5b6cff;
  --brand-2: #00c2a8;
  --good: #1eb980;
  --good-bg: #e3f9ee;
  --bad: #ef5b6b;
  --bad-bg: #fde7ea;
  --warn: #ffb020;
  --line: #e6ebf3;
  --shadow: 0 10px 30px rgba(31, 42, 68, 0.10);
  --radius: 18px;
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  font-family: 'Nunito', system-ui, sans-serif;
  background: radial-gradient(1200px 600px at 100% -10%, #e9ecff 0%, transparent 60%),
              radial-gradient(900px 500px at -10% 0%, #d7fff6 0%, transparent 55%),
              var(--bg);
  color: var(--ink);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

h1, h2, h3, .brand, .btn { font-family: 'Baloo 2', system-ui, sans-serif; }

/* Top bar */
.topbar {
  display: flex; align-items: center; justify-content: space-between;
  padding: 14px 22px; background: rgba(255,255,255,0.8);
  backdrop-filter: blur(8px); border-bottom: 1px solid var(--line);
  position: sticky; top: 0; z-index: 10;
}
.brand { font-size: 22px; font-weight: 800; color: var(--brand); cursor: pointer; }
.countdown {
  font-weight: 800; color: #fff; background: linear-gradient(135deg, var(--brand), var(--brand-2));
  padding: 7px 14px; border-radius: 999px; font-size: 14px; box-shadow: var(--shadow);
}

main { flex: 1; width: 100%; max-width: 880px; margin: 0 auto; padding: 24px 18px 60px; }

.footer { text-align: center; color: var(--muted); padding: 18px; font-size: 13px; }

/* Buttons */
.btn {
  border: none; border-radius: 14px; padding: 13px 20px; font-size: 16px; font-weight: 700;
  cursor: pointer; transition: transform .08s ease, box-shadow .2s ease, background .2s ease;
  background: linear-gradient(135deg, var(--brand), #7a86ff); color: #fff; box-shadow: var(--shadow);
}
.btn:hover { transform: translateY(-2px); }
.btn:active { transform: translateY(0); }
.btn.secondary { background: #fff; color: var(--brand); border: 2px solid var(--line); box-shadow: none; }
.btn.ghost { background: transparent; color: var(--muted); box-shadow: none; }
.btn.big { width: 100%; padding: 16px; font-size: 18px; }
.btn:disabled { opacity: .5; cursor: not-allowed; transform: none; }

/* Cards */
.card {
  background: var(--card); border-radius: var(--radius); box-shadow: var(--shadow);
  padding: 22px; margin-bottom: 16px; border: 1px solid var(--line);
}

/* Home hero */
.hero { text-align: center; padding: 26px 22px; }
.hero h1 { font-size: 34px; margin: 6px 0; }
.hero p { color: var(--muted); font-size: 17px; margin: 6px 0 18px; }

/* Topic grid */
.grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(230px, 1fr)); gap: 14px; }
.topic-card {
  background: var(--card); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 18px; cursor: pointer; transition: transform .1s ease, box-shadow .2s ease;
  position: relative; box-shadow: 0 4px 14px rgba(31,42,68,.06);
}
.topic-card:hover { transform: translateY(-3px); box-shadow: var(--shadow); }
.topic-card .day { font-size: 12px; font-weight: 800; color: var(--brand); text-transform: uppercase; letter-spacing: .5px; }
.topic-card h3 { margin: 6px 0 4px; font-size: 18px; }
.topic-card .emoji { font-size: 28px; }
.topic-card .done-badge { position: absolute; top: 14px; right: 14px; font-size: 20px; }
.progress-wrap { height: 8px; background: #eef1f7; border-radius: 999px; overflow: hidden; margin-top: 10px; }
.progress-bar { height: 100%; background: linear-gradient(90deg, var(--good), var(--brand-2)); width: 0%; transition: width .4s ease; }
.best { font-size: 12px; color: var(--muted); margin-top: 6px; }

/* Lesson content */
.lesson h2 { margin-top: 0; }
.lesson h3 { color: var(--brand); margin: 20px 0 6px; }
.lesson p { line-height: 1.6; font-size: 16px; }
.lesson ul { line-height: 1.7; }
.example {
  background: #f3f6ff; border-left: 4px solid var(--brand); border-radius: 10px;
  padding: 10px 14px; margin: 10px 0; font-size: 16px;
}
.tip { background: var(--good-bg); border-left: 4px solid var(--good); border-radius: 10px; padding: 10px 14px; margin: 10px 0; }
.lesson h4 { margin: 16px 0 4px; font-size: 16px; color: var(--ink); }
.worked { background: #f3f6ff; border-left: 4px solid var(--brand); border-radius: 10px; padding: 11px 14px; margin: 10px 0; line-height: 1.7; font-size: 16px; }
.worked b.ans { color: var(--good); }
.pitfall { background: #fff4e8; border-left: 4px solid var(--warn); border-radius: 10px; padding: 10px 14px; margin: 12px 0; line-height: 1.6; }
table.convert { width: 100%; border-collapse: collapse; margin: 12px 0; }
table.convert th, table.convert td { border: 1px solid var(--line); padding: 8px 10px; text-align: center; }
table.convert th { background: #f3f6ff; }
.frac { display: inline-flex; flex-direction: column; text-align: center; vertical-align: middle; margin: 0 2px; }
.frac .top { border-bottom: 2px solid currentColor; padding: 0 4px; }
.frac .bot { padding: 0 4px; }

/* Quiz */
.quiz-head { display: flex; align-items: center; justify-content: space-between; margin-bottom: 8px; }
.qcount { font-weight: 800; color: var(--muted); }
.score-pill { font-weight: 800; background: #f3f6ff; color: var(--brand); padding: 5px 12px; border-radius: 999px; }
.qbar-wrap { height: 10px; background: #eef1f7; border-radius: 999px; overflow: hidden; margin-bottom: 18px; }
.qbar { height: 100%; background: linear-gradient(90deg, var(--brand), var(--brand-2)); transition: width .3s ease; }
.question { font-size: 22px; font-weight: 700; margin: 6px 0 18px; line-height: 1.4; }
.choices { display: grid; gap: 10px; }
.choice {
  text-align: left; padding: 14px 16px; border-radius: 14px; border: 2px solid var(--line);
  background: #fff; font-size: 17px; font-weight: 600; cursor: pointer; transition: all .12s ease;
  font-family: 'Nunito', sans-serif; color: var(--ink);
}
.choice:hover { border-color: var(--brand); background: #f7f9ff; }
.choice.correct { border-color: var(--good); background: var(--good-bg); }
.choice.wrong { border-color: var(--bad); background: var(--bad-bg); }
.choice.selected { border-color: var(--brand); background: #eef1ff; }
.choice:disabled { cursor: default; }

/* Question palette (jump to any question) */
.palette { display: flex; flex-wrap: wrap; gap: 6px; margin: 4px 0 2px; }
.pal {
  width: 36px; height: 36px; border-radius: 9px; border: 2px solid var(--line);
  background: #fff; font-weight: 700; cursor: pointer; color: var(--muted);
  font-family: 'Nunito', sans-serif; font-size: 14px; transition: all .1s ease;
}
.pal:hover { border-color: var(--brand); }
.pal.done { background: #eef1ff; color: var(--brand); border-color: #c9d2ff; }
.pal.cur { border-color: var(--brand); color: var(--brand); box-shadow: 0 0 0 3px rgba(91,108,255,.18); }
.answer-row { display: flex; gap: 10px; }
.answer-input {
  flex: 1; padding: 14px 16px; border-radius: 14px; border: 2px solid var(--line);
  font-size: 18px; font-family: 'Nunito', sans-serif; font-weight: 700; color: var(--ink);
}
.answer-input:focus { outline: none; border-color: var(--brand); }
.feedback { margin-top: 16px; padding: 14px 16px; border-radius: 14px; font-size: 16px; line-height: 1.55; }
.feedback.ok { background: var(--good-bg); border: 1px solid var(--good); }
.feedback.no { background: var(--bad-bg); border: 1px solid var(--bad); }
.feedback .label { font-weight: 800; font-family: 'Baloo 2', sans-serif; }
.hint { color: var(--muted); font-size: 14px; margin-top: 8px; }

/* Results */
.result { text-align: center; padding: 30px 20px; }
.result .big-emoji { font-size: 64px; }
.result h2 { font-size: 30px; margin: 8px 0; }
.result .scoreline { font-size: 22px; font-weight: 800; color: var(--brand); }

.row { display: flex; gap: 10px; flex-wrap: wrap; }
.row > * { flex: 1; min-width: 140px; }
.center { text-align: center; }
.mt { margin-top: 16px; }
.muted { color: var(--muted); }
.back { display: inline-flex; align-items: center; gap: 6px; cursor: pointer; color: var(--muted); font-weight: 700; margin-bottom: 12px; }
.back:hover { color: var(--brand); }
.kbd { background:#eef1f7; border-radius:6px; padding:1px 7px; font-weight:700; font-size:14px; }