:root {
  --bg: #f7f7f5; --panel: #ffffff; --ink: #1d1d1f; --muted: #6b6b70; --line: #e3e3e0;
  --accent: #2f5bd3; --good: #1f8a4c; --bad: #c6372c; --warn: #b7791f; --chip: #eef1f8;
}
@media (prefers-color-scheme: dark) {
  :root { --bg: #151517; --panel: #1f1f22; --ink: #ececef; --muted: #9a9aa2; --line: #333338;
          --accent: #7b9cff; --good: #4cc27f; --bad: #ff6b5e; --warn: #e3a947; --chip: #2a2d38; }
}
* { box-sizing: border-box; }
body { margin: 0; background: var(--bg); color: var(--ink); font: 16px/1.55 -apple-system, "Segoe UI", Roboto, sans-serif; }
header { position: sticky; top: 0; z-index: 5; display: flex; align-items: center; gap: 16px; flex-wrap: wrap;
  padding: 10px 20px; background: var(--panel); border-bottom: 1px solid var(--line); }
.brand { font-weight: 700; cursor: pointer; }
nav { display: flex; gap: 4px; flex-wrap: wrap; }
nav button, .btn { border: 1px solid var(--line); background: var(--panel); color: var(--ink); padding: 7px 14px;
  border-radius: 8px; cursor: pointer; font: inherit; font-size: 14px; }
nav button.active { background: var(--accent); color: #fff; border-color: var(--accent); }
.btn.primary { background: var(--accent); color: #fff; border-color: var(--accent); }
.btn:disabled { opacity: .45; cursor: default; }
.profile { margin-left: auto; font-size: 13px; color: var(--muted); }
main { max-width: 980px; margin: 0 auto; padding: 20px 16px 80px; }
h1 { font-size: 24px; margin: 6px 0 14px; } h2 { font-size: 19px; margin: 24px 0 10px; } h3 { font-size: 16px; margin: 16px 0 6px; }
.card { background: var(--panel); border: 1px solid var(--line); border-radius: 12px; padding: 18px; margin: 12px 0; }
.muted { color: var(--muted); } .small { font-size: 13px; }
.grid { display: grid; gap: 12px; grid-template-columns: repeat(auto-fit, minmax(170px, 1fr)); }
.stat { background: var(--panel); border: 1px solid var(--line); border-radius: 12px; padding: 14px; }
.stat .v { font-size: 26px; font-weight: 700; } .stat .k { font-size: 13px; color: var(--muted); }
.bar { height: 10px; background: var(--line); border-radius: 6px; overflow: hidden; }
.bar > div { height: 100%; background: var(--good); }
.chips { display: flex; flex-wrap: wrap; gap: 6px; }
.chip { font-size: 13px; padding: 4px 10px; border-radius: 999px; background: var(--chip); border: 1px solid transparent; cursor: pointer; }
.chip.passed { background: color-mix(in srgb, var(--good) 22%, transparent); }
.chip.mastered { background: var(--good); color: #fff; }
.chip.weak { background: color-mix(in srgb, var(--bad) 22%, transparent); border-color: var(--bad); }
.chip.unseen { opacity: .75; }
.legend span { margin-right: 12px; }
.problem { font-size: 17px; }
.problem img.diagram { max-width: 100%; display: block; margin: 10px auto; background: #fff; border-radius: 4px; }
.problem p { margin: 8px 0; }
.choices { display: flex; gap: 8px; margin-top: 16px; flex-wrap: wrap; }
.choices button { width: 56px; height: 44px; font-size: 18px; font-weight: 600; border-radius: 10px; border: 2px solid var(--line);
  background: var(--panel); color: var(--ink); cursor: pointer; }
.choices button.sel { border-color: var(--accent); background: color-mix(in srgb, var(--accent) 18%, transparent); }
.choices button.right { border-color: var(--good); background: color-mix(in srgb, var(--good) 25%, transparent); }
.choices button.wrong { border-color: var(--bad); background: color-mix(in srgb, var(--bad) 25%, transparent); }
.choices .skip { width: auto; padding: 0 14px; font-size: 14px; font-weight: 400; }
.meta { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; font-size: 13px; color: var(--muted); margin-bottom: 8px; }
.tag { padding: 2px 8px; border-radius: 6px; background: var(--chip); font-size: 12px; color: var(--ink); }
.ok { color: var(--good); font-weight: 600; } .no { color: var(--bad); font-weight: 600; }
.note { border-left: 4px solid var(--accent); padding: 8px 12px; background: color-mix(in srgb, var(--accent) 7%, transparent); border-radius: 6px; margin: 10px 0; }
details { margin: 8px 0; } summary { cursor: pointer; color: var(--accent); }
.sol { border-top: 1px dashed var(--line); padding-top: 8px; margin-top: 8px; }
table { width: 100%; border-collapse: collapse; font-size: 14px; }
th, td { text-align: left; padding: 6px 8px; border-bottom: 1px solid var(--line); vertical-align: top; }
.timer { font-variant-numeric: tabular-nums; font-weight: 700; font-size: 18px; }
.timer.low { color: var(--bad); }
.qnav { display: flex; flex-wrap: wrap; gap: 4px; margin: 10px 0; }
.qnav button { width: 36px; height: 32px; border-radius: 6px; border: 1px solid var(--line); background: var(--panel); color: var(--ink); cursor: pointer; font-size: 13px; }
.qnav button.answered { background: color-mix(in srgb, var(--accent) 25%, transparent); }
.qnav button.cur { outline: 2px solid var(--accent); }
.row { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; }
input, select { font: inherit; padding: 6px 8px; border-radius: 8px; border: 1px solid var(--line); background: var(--panel); color: var(--ink); }
a { color: var(--accent); }

/* motivation */
.motiv-row { display: flex; gap: 22px; align-items: center; flex-wrap: wrap; }
.streak { display: flex; gap: 10px; align-items: center; }
.streak .flame { font-size: 34px; filter: grayscale(1); opacity: .5; }
.streak.on .flame { filter: none; opacity: 1; }
.streak .v, .week .v { font-size: 26px; font-weight: 700; line-height: 1; }
.streak .k, .week .k, .goal .k { font-size: 13px; color: var(--muted); }
.goal { flex: 1; min-width: 220px; }
.goal select { padding: 1px 4px; margin-left: 6px; }
.bar.big { height: 14px; margin: 6px 0; }
.wins { list-style: none; padding: 0; margin: 4px 0 0; }
.wins li { padding: 3px 0; font-size: 14px; }
.celebrate { border-color: var(--accent); }
.celebrate.perfect { border-color: var(--good); background: color-mix(in srgb, var(--good) 8%, var(--panel)); }
.celebrate .big { font-size: 17px; font-weight: 600; margin-bottom: 6px; }
.wins-inline { display: flex; flex-wrap: wrap; gap: 6px; margin: 6px 0; }
.win { font-size: 13px; padding: 3px 10px; border-radius: 999px; background: color-mix(in srgb, var(--good) 18%, transparent); }
.win.mastered { background: var(--good); color: #fff; }
.badges { display: grid; gap: 10px; grid-template-columns: repeat(auto-fill, minmax(140px, 1fr)); }
.badge { border: 1px dashed var(--line); border-radius: 12px; padding: 10px; text-align: center; opacity: .45; filter: grayscale(1); }
.badge.got { opacity: 1; filter: none; border-style: solid; border-color: var(--good); background: var(--panel); }
.badge .bi { font-size: 28px; } .badge .bn { font-weight: 600; font-size: 13px; } .badge .bd { font-size: 11px; color: var(--muted); }
#toasts { position: fixed; bottom: 20px; left: 50%; transform: translateX(-50%); z-index: 50; display: flex; flex-direction: column; gap: 8px; align-items: center; }
.toast { background: var(--panel); border: 2px solid var(--good); border-radius: 12px; padding: 10px 18px; box-shadow: 0 6px 24px rgba(0,0,0,.18);
  animation: pop .3s ease-out; transition: opacity .5s, transform .5s; text-align: center; }
.toast.out { opacity: 0; transform: translateY(10px); }
@keyframes pop { from { transform: scale(.8); opacity: 0; } to { transform: scale(1); opacity: 1; } }
canvas.confetti { position: fixed; inset: 0; pointer-events: none; z-index: 40; }