/* Arithmetic drill — the example is written in a squared school notebook */

:root {
  --ink: #3d2b2f;
  --muted: #8b7576;
  --sky: #d7f0ff;
  --cream: #fff8ec;
  --line: #cfe3f5;         /* notebook grid */
  --ok: #22a35a;
  --ok-bg: #dcf8e7;
  --bad: #e5484d;
  --bad-bg: #ffe4e4;
  --border: #eadfcd;
  --gold: #f5b301;         /* stars */
  --accent: #ff7096;       /* each operation has its own colour, see body[data-op] */
  --accent-dark: #e04f78;
  --accent-soft: #ffe1ea;
}

body[data-op="sub"] { --accent: #4aa3df; --accent-dark: #2f86c0; --accent-soft: #dcefff; }
body[data-op="mul"] { --accent: #f2a516; --accent-dark: #d18a00; --accent-soft: #fff1c9; }
body[data-op="div"] { --accent: #9b7be0; --accent-dark: #7c5cc4; --accent-soft: #ece5ff; }
body[data-op="mix"] { --accent: #2bb3a3; --accent-dark: #1f8f82; --accent-soft: #d5f4f0; }
body[data-op="eq"] { --accent: #5b6ee1; --accent-dark: #4153c4; --accent-soft: #e3e7ff; }

* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  background: linear-gradient(180deg, var(--sky) 0%, var(--cream) 55%) fixed;
  color: var(--ink);
  font-family: "Nunito", ui-rounded, "SF Pro Rounded", system-ui, -apple-system, sans-serif;
  font-weight: 600;
  -webkit-tap-highlight-color: transparent;
  /* Notebook cell size; --cols (cells across the paper) is set on body from the script */
  --cell: min(88px, calc((100vw - 32px) / var(--cols, 8)));
}

button {
  font: inherit;
  color: inherit;
  cursor: pointer;
}
button:disabled { cursor: default; }

/* ---------- Score ---------- */

header { padding: 14px 16px 0; display: flex; flex-direction: column; align-items: center; gap: 12px; }

/* ---------- Levels ---------- */

.levels {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 10px;
}

.level {
  display: grid;
  grid-template-columns: auto auto;
  grid-template-areas: "num name" "num stars";
  align-items: center;
  column-gap: 10px;
  padding: 6px 16px 6px 8px;
  background: rgba(255, 255, 255, 0.7);
  border: 3px solid transparent;
  border-radius: 18px;
  text-align: left;
  transition: transform 0.15s, background 0.15s;
}
.level:hover { transform: translateY(-2px); }
.level.current { background: #fff; border-color: var(--accent); box-shadow: 0 4px 0 var(--accent-soft); }
.level-num {
  grid-area: num;
  display: grid;
  place-items: center;
  width: 38px;
  height: 38px;
  border-radius: 50%;
  background: var(--accent-soft);
  color: var(--accent-dark);
  font-size: 22px;
  font-weight: 900;
}
.level.current .level-num { background: var(--accent); color: #fff; }
.level-name { grid-area: name; font-size: 16px; font-weight: 800; white-space: nowrap; }

.stars { grid-area: stars; display: flex; gap: 1px; font-size: 15px; line-height: 1; }
.stars i { font-style: normal; color: #e7ddd0; }
.stars i.on { color: var(--gold); }
.stars.big { justify-content: center; gap: 6px; margin-bottom: 10px; font-size: 40px; }
.stars.big i.on { animation: pop 0.4s ease-out both; }
.stars.big i:nth-child(2) { animation-delay: 0.15s; }
.stars.big i:nth-child(3) { animation-delay: 0.3s; }

/* ---------- Score ---------- */

.score {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 10px;
}

.chip {
  padding: 6px 16px;
  background: rgba(255, 255, 255, 0.75);
  border-radius: 999px;
  font-size: 20px;
  font-weight: 800;
  font-variant-numeric: tabular-nums;
}

/* ---------- Notebook paper ---------- */

main {
  max-width: 1100px;
  margin: 0 auto;
  padding: 28px 16px 90px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
}

.paper {
  display: grid;
  grid-template-columns: repeat(var(--cols, 8), var(--cell));
  grid-template-rows: repeat(var(--rows, 3), var(--cell)); /* 4 with fractions: numerators and denominators */
  background:
    linear-gradient(to right, var(--line) 1px, transparent 1px) 0 0 / var(--cell) var(--cell),
    linear-gradient(to bottom, var(--line) 1px, transparent 1px) 0 0 / var(--cell) var(--cell),
    #fff;
  border-radius: calc(var(--cell) * 0.25);
  box-shadow: 0 6px 0 var(--accent-soft), 0 10px 24px rgba(61, 43, 47, 0.08);
  overflow: hidden;
}

.cell {
  display: grid;
  place-items: center;
  font-size: calc(var(--cell) * 0.82);
  font-weight: 900;
  line-height: 1;
}

.answer {
  margin: 2px;
  border: 4px solid var(--accent);
  border-radius: calc(var(--cell) * 0.18);
  background: color-mix(in srgb, var(--accent-soft) 60%, transparent);
}
/* A fraction: numerator, bar, denominator. On the paper each takes a row and the bar lies on the grid line */
.frac {
  display: inline-grid;
  grid-template-rows: auto auto;
  justify-items: center;
  line-height: 1.05;
}
.frac > span + span { border-top: 0.09em solid currentColor; padding-top: 0.04em; }
.paper .frac {
  width: 100%;
  height: 100%;
  grid-template-rows: 1fr 1fr;
  align-items: center;
  font-size: 0.86em;
}
.paper .frac > span { width: 100%; display: grid; place-items: center; height: 100%; }
.paper .frac > span + span { padding-top: 0; border-top-width: 3px; }

.answer.unknown { color: var(--accent-dark); font-style: italic; }
.answer.ok { border-color: var(--ok); background: var(--ok-bg); color: var(--ok); animation: pop 0.3s ease-out; }
.answer.bad { border-color: var(--bad); background: var(--bad-bg); animation: pop 0.3s ease-out; }

/* ---------- Timer ---------- */

.timer {
  width: calc(var(--cell) * var(--cols, 8));
  height: 14px;
  background: var(--border);
  border-radius: 999px;
  overflow: hidden;
}
.timer-fill {
  height: 100%;
  background: var(--accent);
  border-radius: inherit;
  transform-origin: left;
}
.timer-fill.hurry { background: var(--bad); }

#message { margin: 0; min-height: 1.4em; font-size: 28px; font-weight: 900; text-align: center; }
#message.ok { color: var(--ok); animation: pop 0.3s ease-out; }
#message.info { color: var(--muted); font-size: 20px; font-weight: 800; }
#message.bad { color: var(--bad); }

/* ---------- Answers ---------- */

.options {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 150px));
  gap: 16px;
  width: 100%;
  justify-content: center;
}

.option {
  padding: 16px 0;
  font-size: 52px;
  font-weight: 900;
  line-height: 1.1;
  font-variant-numeric: tabular-nums;
  background: #fff;
  border: 4px solid var(--accent-soft);
  border-radius: 24px;
  box-shadow: 0 6px 0 var(--accent);
  transition: transform 0.1s, box-shadow 0.1s, opacity 0.2s;
}
.option:hover:not(:disabled) { transform: translateY(-3px); }
.option:active:not(:disabled) { transform: translateY(5px); box-shadow: 0 1px 0 var(--accent); }
.option:disabled { color: var(--ink); }
.option .frac { font-size: 0.68em; }
.option.ok { border-color: var(--ok); background: var(--ok-bg); color: var(--ok); box-shadow: 0 6px 0 var(--ok); }
.option.bad { border-color: var(--bad); background: var(--bad-bg); color: var(--bad); box-shadow: 0 6px 0 var(--bad); }
.option.dim { opacity: 0.35; }

.btn.start { grid-column: 1 / -1; justify-self: center; font-size: 30px; padding: 16px 48px; }

/* ---------- Start and results dialogs ---------- */

.btn {
  font-size: 21px;
  font-weight: 800;
  padding: 12px 30px;
  border-radius: 999px;
  border: 3px solid var(--border);
  background: #fff;
  box-shadow: 0 4px 0 var(--border);
  transition: transform 0.1s, box-shadow 0.1s;
}
.btn:active { transform: translateY(3px); box-shadow: 0 1px 0 var(--border); }
.btn.primary { background: var(--accent); border-color: var(--accent); color: #fff; box-shadow: 0 4px 0 var(--accent-dark); }
.btn.primary:active { box-shadow: 0 1px 0 var(--accent-dark); }

.overlay {
  position: fixed;
  inset: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 16px;
  background: rgba(61, 43, 47, 0.35);
}
.overlay[hidden] { display: none; }
.card {
  max-width: 440px;
  width: 100%;
  padding: 28px 24px;
  background: #fff;
  border-radius: 28px;
  text-align: center;
  box-shadow: 0 10px 0 var(--accent-soft), 0 20px 50px rgba(0, 0, 0, 0.2);
  animation: pop 0.35s ease-out;
}
.card-icon { font-size: 84px; line-height: 1.1; }
.card h2 { margin: 10px 0 8px; font-size: 30px; font-weight: 900; }
.card p { margin: 0 0 22px; color: var(--muted); font-size: 18px; }
.card-buttons { display: flex; flex-wrap: wrap; justify-content: center; gap: 12px; }
.card-buttons [hidden] { display: none; }

/* ---------- Confetti ---------- */

.confetti { position: fixed; inset: 0; pointer-events: none; overflow: hidden; z-index: 20; }
.confetti span { position: absolute; top: -50px; animation: fall 1.8s ease-in forwards; }

/* ---------- Animations ---------- */

@keyframes pop { 0% { transform: scale(0.85); } 70% { transform: scale(1.06); } 100% { transform: scale(1); } }
@keyframes fall {
  to { transform: translate(var(--drift, 0), 110vh) rotate(540deg); opacity: 0.9; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation: none !important; transition: none !important; }
}

/* ---------- Phone ---------- */

@media (max-width: 700px) {
  header { padding: 10px 8px 0; gap: 8px; }
  .levels { gap: 6px; }
  .level { grid-template-columns: auto; grid-template-areas: "num" "stars"; justify-items: center; row-gap: 3px; padding: 5px 10px; }
  .level-name { display: none; }
  .level-num { width: 32px; height: 32px; font-size: 19px; }
  .stars { font-size: 13px; }
  #message.info { font-size: 17px; }
  .btn.start { font-size: 26px; padding: 14px 40px; }
  .score { gap: 6px; }
  .chip { font-size: 16px; padding: 4px 11px; }
  main { padding: 18px 16px 70px; gap: 12px; }
  .timer { height: 10px; }
  #message { font-size: 21px; }
  .options { grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 12px; max-width: 400px; }
  .option { font-size: 44px; padding: 12px 0; border-radius: 20px; }
}