/* Squared exercise-notebook paper. The grid is the page, not decoration --
   it's the material a Class 6 student actually does sums on. */
:root {
  --paper:      #F7FAF9;
  --grid:       #DDE9E6;
  --grid-major: #C7DAD6;
  --card:       #FFFFFF;
  --ink:        #14324D;
  --ink-soft:   #526B7E;
  --ink-faint:  #8CA0AD;
  --rule:       #DCE6EA;
  --tick:       #1F7A4C;
  --tick-bg:    #E8F4ED;
  --cross:      #C0392B;
  --cross-bg:   #FBECEA;
  --gold:       #C68B14;
  --radius:     10px;
  --shadow:     0 1px 2px rgba(20,50,77,.06), 0 8px 24px rgba(20,50,77,.05);
}

* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  font: 400 16px/1.6 ui-sans-serif, system-ui, "Segoe UI", Roboto, sans-serif;
  color: var(--ink);
  background-color: var(--paper);
  background-image:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px),
    linear-gradient(var(--grid-major) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid-major) 1px, transparent 1px);
  background-size: 24px 24px, 24px 24px, 120px 120px, 120px 120px;
}

.wrap { max-width: 760px; margin: 0 auto; padding: 32px 20px 80px; }

h1, h2, h3 { margin: 0 0 4px; font-weight: 600; letter-spacing: -0.02em; line-height: 1.2; }
h1 { font-size: 30px; }
h2 { font-size: 21px; }
h3 { font-size: 17px; }
p  { margin: 0 0 12px; }
.muted { color: var(--ink-soft); font-size: 14px; }
.num { font-variant-numeric: tabular-nums; }

header.site {
  display: flex; align-items: baseline; justify-content: space-between;
  gap: 16px; flex-wrap: wrap; margin-bottom: 28px;
  padding-bottom: 16px; border-bottom: 2px solid var(--ink);
}
header.site .who { font-size: 14px; color: var(--ink-soft); }

.card {
  background: var(--card); border: 1px solid var(--rule);
  border-radius: var(--radius); padding: 20px; margin-bottom: 16px;
  box-shadow: var(--shadow);
}

/* --- controls ------------------------------------------------------------ */
button {
  font: inherit; font-weight: 500; cursor: pointer;
  border-radius: var(--radius); border: 1px solid transparent;
  padding: 10px 18px; transition: background .12s, border-color .12s;
}
.btn-primary { background: var(--ink); color: #fff; }
.btn-primary:hover { background: #0D2439; }
.btn-quiet { background: transparent; color: var(--ink); border-color: var(--rule); }
.btn-quiet:hover { border-color: var(--ink-faint); }
button:disabled { opacity: .45; cursor: not-allowed; }
button:focus-visible, a:focus-visible, input:focus-visible {
  outline: 2px solid var(--gold); outline-offset: 2px;
}

label { display: block; font-size: 14px; font-weight: 500; margin: 12px 0 5px; }
input {
  font: inherit; width: 100%; padding: 10px 12px;
  border: 1px solid var(--rule); border-radius: var(--radius);
  background: var(--paper); color: var(--ink);
}
.row { display: flex; gap: 10px; flex-wrap: wrap; align-items: center; }
.err   { color: var(--cross); font-size: 14px; margin-top: 10px; }
.notice{ color: var(--tick);  font-size: 14px; margin-top: 10px; }

/* --- signature: the marking strip ---------------------------------------
   25 boxes, one per question, filled like a teacher marking a worksheet.
   Doubles as progress bar and score -- the child can see the shape of the
   attempt at a glance without reading a number. */
.marks { display: flex; gap: 3px; flex-wrap: wrap; margin: 4px 0 14px; }
.mark {
  width: 22px; height: 22px; border-radius: 3px;
  border: 1px solid var(--rule); background: var(--paper);
  display: grid; place-items: center;
  font-size: 13px; font-weight: 600; line-height: 1;
}
.mark.right { background: var(--tick-bg);  border-color: var(--tick);  color: var(--tick); }
.mark.wrong { background: var(--cross-bg); border-color: var(--cross); color: var(--cross); }
.mark.now   { border-color: var(--ink); border-width: 2px; }

/* --- chapters and levels ------------------------------------------------- */
.chapter { display: flex; justify-content: space-between; gap: 16px; flex-wrap: wrap; align-items: center; }
.levels { display: flex; gap: 8px; }
.level {
  min-width: 92px; text-align: left; padding: 8px 12px;
  border: 1px solid var(--rule); border-radius: var(--radius);
  background: var(--paper); color: var(--ink);
}
.level:hover:not(:disabled) { border-color: var(--ink); }
.level .lv { display: block; font-size: 12px; color: var(--ink-soft); }
.level .st { display: block; font-size: 14px; font-weight: 600; }
.level.passed { background: var(--tick-bg); border-color: var(--tick); }
.level.passed .st { color: var(--tick); }
.level.locked { color: var(--ink-faint); }
.level.locked .st { color: var(--ink-faint); }

/* --- question ------------------------------------------------------------ */
.stem { font-size: 20px; font-weight: 500; margin: 6px 0 18px; line-height: 1.45; }
.opts { display: grid; gap: 8px; }
.opt {
  display: flex; align-items: center; gap: 12px; text-align: left; width: 100%;
  padding: 14px 16px; background: var(--card);
  border: 1px solid var(--rule); border-radius: var(--radius); color: var(--ink);
  font-weight: 400; font-size: 17px;
}
.opt:hover:not(:disabled) { border-color: var(--ink); background: var(--paper); }
.opt .key {
  flex: none; width: 26px; height: 26px; border-radius: 50%;
  border: 1px solid var(--ink-faint); display: grid; place-items: center;
  font-size: 13px; font-weight: 600; text-transform: uppercase;
}
.opt.right { background: var(--tick-bg);  border-color: var(--tick); }
.opt.right .key { border-color: var(--tick); background: var(--tick); color: #fff; }
.opt.wrong { background: var(--cross-bg); border-color: var(--cross); }
.opt.wrong .key { border-color: var(--cross); background: var(--cross); color: #fff; }

.explain {
  margin-top: 16px; padding: 14px 16px; border-radius: var(--radius);
  background: var(--paper); border-left: 3px solid var(--gold); border-radius: 0 var(--radius) var(--radius) 0;
}
.explain b { display: block; font-size: 13px; text-transform: uppercase;
  letter-spacing: .06em; color: var(--gold); margin-bottom: 4px; font-weight: 600; }

.score-big { font-size: 52px; font-weight: 600; letter-spacing: -.03em; line-height: 1; }
.score-big span { font-size: 22px; color: var(--ink-soft); font-weight: 400; }

table { width: 100%; border-collapse: collapse; font-size: 15px; }
th, td { text-align: left; padding: 8px 10px; border-bottom: 1px solid var(--rule); }
th { font-size: 12px; text-transform: uppercase; letter-spacing: .06em; color: var(--ink-soft); font-weight: 600; }
td.n, th.n { text-align: right; font-variant-numeric: tabular-nums; }
.rank { color: var(--ink-faint); font-variant-numeric: tabular-nums; }

.tabs { display: flex; gap: 6px; margin-bottom: 14px; flex-wrap: wrap; }
.tab { padding: 6px 14px; font-size: 14px; border-radius: 999px;
  border: 1px solid var(--rule); background: var(--paper); color: var(--ink-soft); }
.tab[aria-selected="true"] { background: var(--ink); color: #fff; border-color: var(--ink); }

.hide { display: none !important; }

/* Honeypot. Off-screen rather than display:none, because some bots skip
   display:none fields. Hidden from assistive tech via aria-hidden. */
.hp { position: absolute; left: -9999px; width: 1px; height: 1px; overflow: hidden; }

.card.danger { border-color: #EBC7C3; }
.card.danger h3 { color: var(--cross); }
.btn-danger { background: var(--cross); color: #fff; }
.btn-danger:hover { background: #A32E22; }

@media (max-width: 540px) {
  h1 { font-size: 25px; }
  .stem { font-size: 18px; }
  .mark { width: 19px; height: 19px; font-size: 11px; }
  .levels { width: 100%; }
  .level { flex: 1; min-width: 0; }
}
@media (prefers-reduced-motion: reduce) { * { transition: none !important; } }