/* Nota 10 — «тетрадь в клетку»: бумага в клетку, синие чернила, красная линия полей. */
:root {
  --paper: #fcfdff; --grid: #e4ecf7; --ink: #1d3a7a; --text: #22252b; --muted: #5d6675;
  --margin: #e26a6a; --right: #1f7a4a; --right-bg: #e3f4ea; --wrong: #c2412d; --wrong-bg: #fbe7e3;
  --line: #cfd9e8; --cell: 22px;
}
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0; color: var(--text); font: 18px/1.55 "Source Sans 3", "Segoe UI", system-ui, sans-serif;
  background-color: var(--paper);
  background-image: linear-gradient(var(--grid) 1px, transparent 1px), linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size: var(--cell) var(--cell);
}
h1, h2 { font-family: Bitter, Georgia, serif; color: var(--ink); line-height: 1.2; }
h1 { font-size: 2rem; margin: 0 0 .5rem; }
h2 { font-size: 1.3rem; margin: 2rem 0 .6rem; }
a { color: var(--ink); }
:focus-visible { outline: 3px solid #f2b705; outline-offset: 2px; }

/* верхняя полоса */
nav.top { display: flex; align-items: center; gap: 1.2rem; padding: .6rem 1.2rem; background: var(--ink); color: #fff; flex-wrap: wrap; }
nav.top a { color: #e7edfb; text-decoration: none; }
nav.top a[aria-current] { color: #fff; text-decoration: underline; text-underline-offset: 4px; }
nav.top .brand { font-family: Bitter, serif; font-weight: 700; font-size: 1.25rem; color: #fff; }
nav.top .links { display: flex; gap: 1rem; flex-wrap: wrap; }
nav.top .out { margin-left: auto; }
button.link { background: none; border: 0; color: #e7edfb; font: inherit; cursor: pointer; padding: 0; }

/* лист тетради: красная линия полей слева — главный образ интерфейса */
main.sheet { max-width: 760px; margin: 1.5rem auto 4rem; padding: 1.5rem 1.5rem 2rem 3.2rem; position: relative; }
main.sheet::before { content: ""; position: absolute; left: 1.8rem; top: 0; bottom: 0; width: 2px; background: var(--margin); opacity: .75; }
body.admin main.sheet { max-width: 1060px; }
body.admin main.sheet::before { display: none; }
body.admin main.sheet { padding-left: 1.5rem; background: rgba(252, 253, 255, .94); }

.lead, .today { color: var(--muted); margin-top: 0; }
.meta { color: var(--muted); font-size: .95rem; margin: 0 0 .6rem; }
.small { color: var(--muted); font-size: .9rem; }
.back { margin: 0 0 .4rem; font-size: .95rem; }

/* главная */
.choices { display: grid; gap: .9rem; margin-top: 1.5rem; }
.choice { display: block; padding: 1rem 1.2rem; background: #fff; border: 2px solid var(--ink); border-radius: 6px;
  text-decoration: none; font-family: Bitter, serif; font-size: 1.25rem; color: var(--ink); }
.choice small { display: block; font-family: "Source Sans 3", sans-serif; font-size: .95rem; color: var(--muted); }
.choice.main { background: var(--ink); color: #fff; }
.choice.main small { color: #d6def2; }

/* задание */
article.task { background: #fff; border: 1px solid var(--line); border-radius: 4px; padding: 1.1rem 1.3rem; }
.statement { margin: 0 0 .8rem; font-size: 1.1rem; }
img.fig, img.orig { display: block; max-width: 100%; height: auto; margin: .8rem auto; }
img.fig { max-height: 360px; }
.tablewrap { overflow-x: auto; }
table.data { border-collapse: collapse; margin: .6rem 0 1rem; background: #fff; }
table.data th, table.data td { border: 1px solid var(--line); padding: .35rem .8rem; text-align: center; }
table.data th { background: #eef3fb; font-weight: 600; }

.opts { display: grid; grid-template-columns: repeat(auto-fit, minmax(150px, 1fr)); gap: .7rem; margin: 1.2rem 0; }
.opt { display: flex; align-items: center; gap: .7rem; padding: .7rem .9rem; border: 2px solid var(--line); border-radius: 6px;
  background: #fff; font: inherit; color: var(--text); text-align: left; min-height: 3.2rem; }
button.opt { cursor: pointer; }
button.opt:hover { border-color: var(--ink); }
.letter { flex: none; width: 2rem; height: 2rem; border-radius: 50%; display: grid; place-items: center;
  border: 2px solid var(--ink); color: var(--ink); font-weight: 600; }
.opt.right { border-color: var(--right); background: var(--right-bg); }
.opt.right .letter { background: var(--right); border-color: var(--right); color: #fff; }
.opt.wrong { border-color: var(--wrong); background: var(--wrong-bg); }
.opt.wrong .letter { background: var(--wrong); border-color: var(--wrong); color: #fff; }
.opt.dim { opacity: .55; }
.verdict { font-family: Bitter, serif; font-size: 1.25rem; margin: .2rem 0 1rem; }
.verdict.ok { color: var(--right); }
.verdict.no { color: var(--wrong); }

/* объяснение — как запись учителя на полях */
.explain { border-left: 4px solid var(--ink); background: #fff; padding: .8rem 1.1rem; margin: 1rem 0; }
.explain h2 { margin-top: 0; }
.idea { font-weight: 600; }
.steps { padding-left: 1.3rem; }
.steps li { margin: .25rem 0; }
.why { background: var(--wrong-bg); padding: .6rem .8rem; border-radius: 4px; }
.rulelinks { display: flex; flex-wrap: wrap; gap: .5rem; align-items: center; margin-top: .6rem; }
.rulelinks span { color: var(--muted); font-size: .95rem; }
.rulelink { padding: .2rem .65rem; border: 1px solid var(--ink); border-radius: 999px; text-decoration: none; font-size: .95rem; }

.actions { display: flex; gap: .7rem; flex-wrap: wrap; margin: 1.2rem 0; }
.btn, .btn2 { display: inline-block; font: inherit; font-weight: 600; padding: .6rem 1.2rem; border-radius: 6px; cursor: pointer; text-decoration: none; }
.btn { background: var(--ink); color: #fff; border: 2px solid var(--ink); }
.btn2 { background: #fff; color: var(--ink); border: 2px solid var(--ink); }
.btn2.danger { color: var(--wrong); border-color: var(--wrong); }
form.inline { display: inline; }

details.report { margin-top: 2rem; color: var(--muted); }
details.report summary { cursor: pointer; }
details.report textarea { display: block; width: 100%; min-height: 5rem; margin: .6rem 0; font: inherit; padding: .5rem; border: 1px solid var(--line); border-radius: 4px; }
.flash, .notice { background: var(--right-bg); border-left: 4px solid var(--right); padding: .6rem .9rem; }
.error { background: var(--wrong-bg); border-left: 4px solid var(--wrong); padding: .6rem .9rem; }
code.pw { font-size: 1.3rem; padding: .1rem .5rem; background: #fff; border: 1px dashed var(--ink); user-select: all; }

/* темы и прогресс */
ul.topics, ul.rulelist, ul.progress { list-style: none; padding: 0; margin: 1rem 0; }
ul.topics li, ul.rulelist li { display: flex; align-items: baseline; gap: .8rem; padding: .55rem 0; border-bottom: 1px solid var(--line); }
ul.topics li a, ul.rulelist li a { flex: 1; text-decoration: none; font-size: 1.05rem; }
.count { color: var(--muted); font-size: .9rem; }
.score { min-width: 3rem; text-align: right; font-weight: 600; color: var(--ink); }
.score.none { color: var(--muted); font-weight: 400; }
ul.progress li { display: grid; grid-template-columns: 1fr 140px 3.5rem auto; gap: .8rem; align-items: center; padding: .45rem 0; border-bottom: 1px solid var(--line); }
.bar { height: .7rem; background: var(--wrong-bg); border-radius: 999px; overflow: hidden; }
.bar i { display: block; height: 100%; background: var(--right); }
.num { color: var(--muted); font-size: .9rem; text-align: right; }

/* правило */
article.rule { background: #fff; border: 1px solid var(--line); padding: 1.1rem 1.3rem; border-radius: 4px; }
img.rulepic { display: block; max-width: 100%; height: auto; max-height: 380px; margin: .8rem auto; }
.plain { background: #eef3fb; padding: .7rem .9rem; border-radius: 4px; margin: .8rem 0; }
.formula { font-size: 1.15rem; color: var(--ink); font-weight: 600; }

/* вход */
.login { max-width: 380px; margin: 3rem auto; background: #fff; padding: 1.6rem; border: 1px solid var(--line); border-radius: 6px; }
.login label, form.grid label { display: block; margin: .8rem 0; font-weight: 600; }
.login input, form.grid input, form.grid select { display: block; width: 100%; font: inherit; padding: .55rem .7rem; margin-top: .3rem; border: 1px solid #b9c6dc; border-radius: 4px; background: #fff; }
.login .btn { width: 100%; margin-top: .6rem; }

/* админка */
form.grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(190px, 1fr)); gap: .2rem 1rem; align-items: end; }
form.grid .btn { margin: .8rem 0; }
table.users { border-collapse: collapse; width: 100%; background: #fff; font-size: .95rem; }
table.users th, table.users td { border-bottom: 1px solid var(--line); padding: .45rem .6rem; text-align: left; vertical-align: top; }
table.users th { background: #eef3fb; }
td.r, th.r { text-align: right; }
tr.off { color: var(--muted); }

@media (max-width: 600px) {
  body { font-size: 17px; }
  main.sheet { padding: 1rem 1rem 2rem 2.2rem; margin-top: .5rem; }
  main.sheet::before { left: 1.1rem; }
  .opts { grid-template-columns: 1fr 1fr; }
  ul.progress li { grid-template-columns: 1fr 80px; }
  ul.progress .num, ul.progress li a { display: none; }
  h1 { font-size: 1.6rem; }
}
@media (prefers-reduced-motion: reduce) { * { transition: none !important; } }