:root {
  --bg: #070b14;
  --bg2: #0b1220;
  --panel: #0f172a;
  --panel2: #131f38;
  --line: #1e293b;
  --line2: #27364f;
  --fg: #e2e8f0;
  --fg2: #94a3b8;
  --fg3: #64748b;
  --acc: #38bdf8;
  --acc2: #0ea5e9;
  --pink: #f472b6;
  --green: #34d399;
  --amber: #fbbf24;
  --red: #f87171;
  --mono: ui-monospace, "SF Mono", "Cascadia Code", Menlo, monospace;
  --sans: system-ui, -apple-system, "Segoe UI", Inter, Roboto, sans-serif;
}

* { box-sizing: border-box; }

html, body {
  margin: 0; padding: 0;
  background: var(--bg);
  color: var(--fg);
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

body.loading .main { opacity: 0; }

/* ---------- layout ---------- */
.shell { display: flex; min-height: 100vh; }

#sidebar {
  width: 290px; flex: 0 0 290px;
  background: linear-gradient(180deg, #0b1220 0%, #080d18 100%);
  border-right: 1px solid var(--line);
  padding: 20px 16px 40px;
  position: sticky; top: 0; height: 100vh; overflow-y: auto;
}
.main { flex: 1; min-width: 0; padding: 32px 40px 100px; max-width: 1200px; }

.brand { margin-bottom: 24px; }
.brand-title { font-size: 1.45rem; font-weight: 800; letter-spacing: -0.02em;
  background: linear-gradient(90deg, var(--acc), var(--pink));
  -webkit-background-clip: text; background-clip: text; color: transparent; }
.brand-sub { font-size: 0.82rem; color: var(--fg3); letter-spacing: 0.08em; text-transform: uppercase; }

.nav { display: flex; flex-direction: column; gap: 4px; margin-bottom: 26px; }
.navbtn {
  display: flex; flex-direction: column; align-items: flex-start; gap: 1px;
  background: transparent; border: 1px solid transparent; color: var(--fg2);
  padding: 9px 12px; border-radius: 10px; cursor: pointer; text-align: left;
  font-family: inherit; font-size: 0.95rem; transition: all .15s;
}
.navbtn:hover { background: var(--panel); color: var(--fg); }
.navbtn.on { background: var(--panel2); border-color: var(--line2); color: var(--fg); }
.nb-l { font-weight: 650; }
.nb-s { font-size: 0.76rem; color: var(--fg3); }

.navsec { font-size: 0.68rem; letter-spacing: 0.14em; color: var(--fg3);
  margin: 0 0 8px 4px; font-weight: 700; }
.tutnav { display: flex; flex-direction: column; gap: 3px; margin-bottom: 24px; }
.tnav {
  background: transparent; border: 1px solid transparent; border-radius: 9px;
  padding: 8px 11px; cursor: pointer; text-align: left; color: var(--fg2);
  font-family: inherit; font-size: 0.88rem; display: block; width: 100%;
  position: relative; transition: all .15s;
}
.tnav:hover { background: var(--panel); color: var(--fg); }
.tnav.on { background: var(--panel2); border-color: var(--acc); color: var(--fg); }
.tnav-l { display: block; font-weight: 600; }
.tnav-s { display: block; font-size: 0.72rem; color: var(--fg3); line-height: 1.35; }
.tnav-d { position: absolute; top: 9px; right: 10px; font-size: 0.68rem;
  font-family: var(--mono); color: var(--fg3); }
.tnav.on .tnav-d { color: var(--acc); }

.progressbox { border-top: 1px solid var(--line); padding-top: 16px; margin-bottom: 16px; }
.pbar { height: 6px; background: var(--line); border-radius: 3px; overflow: hidden; margin: 7px 0 5px; }
.pfill { height: 100%; background: linear-gradient(90deg, var(--acc), var(--green)); transition: width .3s; }

/* ---------- generic ---------- */
h1 { font-size: 1.9rem; margin: 0 0 6px; letter-spacing: -0.02em; font-weight: 750; }
h2 { font-size: 1.18rem; margin: 0 0 10px; letter-spacing: -0.01em; font-weight: 700; }
h3 { font-size: 1.02rem; margin: 26px 0 10px; font-weight: 700; }
p { margin: 0 0 12px; }
code { font-family: var(--mono); font-size: 0.88em; background: var(--panel2);
  padding: 1px 5px; border-radius: 4px; color: #7dd3fc; }
pre { font-family: var(--mono); background: var(--panel); border: 1px solid var(--line);
  border-radius: 8px; padding: 12px 14px; overflow-x: auto; font-size: 0.85rem; }
ul, ol { padding-left: 22px; margin: 0 0 14px; }
li { margin-bottom: 7px; }
b, strong { color: #fff; font-weight: 700; }
.dim { color: var(--fg2); }
.tiny { font-size: 0.78rem; }
.mono { font-family: var(--mono); }

.viewhead { margin-bottom: 26px; }
.viewhead.row { display: flex; align-items: center; justify-content: space-between; gap: 16px; }
.viewhead p { margin: 0; color: var(--fg2); font-size: 0.95rem; }

.btn {
  background: var(--panel2); border: 1px solid var(--line2); color: var(--fg);
  padding: 9px 18px; border-radius: 9px; cursor: pointer; font-family: inherit;
  font-size: 0.9rem; font-weight: 600; transition: all .15s;
}
.btn:hover { border-color: var(--acc); color: #fff; }
.btn.primary { background: linear-gradient(135deg, var(--acc2), #2563eb);
  border-color: transparent; color: #fff; }
.btn.primary:hover { filter: brightness(1.12); }
.btn.ghost { background: transparent; }
.btn.big { padding: 13px 30px; font-size: 1.02rem; }
.btn.wide { width: 100%; }

/* ---------- lesson list ---------- */
.lgrid { display: grid; grid-template-columns: repeat(auto-fill, minmax(320px, 1fr)); gap: 14px; }
.lcard {
  background: var(--panel); border: 1px solid var(--line); border-radius: 14px;
  padding: 16px 18px; cursor: pointer; text-align: left; color: var(--fg);
  font-family: inherit; display: flex; gap: 14px; align-items: flex-start;
  transition: all .16s; position: relative;
}
.lcard:hover { border-color: var(--acc); transform: translateY(-2px);
  box-shadow: 0 8px 26px rgba(56,189,248,.10); }
.lcard.done { border-color: rgba(52,211,153,.35); }
.lc-tut { flex: 0 0 40px; height: 40px; border-radius: 10px; display: grid; place-items: center;
  background: var(--panel2); font-family: var(--mono); font-weight: 700; font-size: .85rem; color: var(--acc); }
.lcard.done .lc-tut { color: var(--green); }
.lc-body { flex: 1; min-width: 0; }
.lc-title { font-weight: 650; margin-bottom: 2px; }
.lc-sub { font-size: 0.83rem; color: var(--fg2); line-height: 1.45; }
.lc-meta { font-size: 0.74rem; color: var(--fg3); margin-top: 7px; }
.lc-check { position: absolute; top: 12px; right: 14px; color: var(--green); font-weight: 700; }

/* ---------- lesson ---------- */
.lessonhead { margin-bottom: 28px; padding-bottom: 18px; border-bottom: 1px solid var(--line); }
.lessonhead h1 { margin-top: 14px; }
.lh-sub { color: var(--fg2); font-size: 1.02rem; margin-bottom: 10px; }
.lh-meta { display: flex; gap: 12px; align-items: center; }
.lessonbody { max-width: 860px; }
.block { margin-bottom: 30px; padding-bottom: 26px; border-bottom: 1px solid rgba(30,41,59,.55); }
.block:last-child { border-bottom: none; }
.bh { color: #fff; }
.bp, .bp2 { color: #cbd5e1; }
.bp2 { margin-top: 8px; padding: 12px 14px; background: var(--panel);
  border-left: 3px solid var(--acc); border-radius: 0 8px 8px 0; font-family: var(--mono); font-size: .88rem; }

.b-note .bp { background: rgba(56,189,248,.07); border-left: 3px solid var(--acc);
  padding: 14px 16px; border-radius: 0 8px 8px 0; }
.b-warn .bp { background: rgba(251,191,36,.08); border-left: 3px solid var(--amber);
  padding: 14px 16px; border-radius: 0 8px 8px 0; }
.b-formula .bp { font-family: var(--mono); font-size: .95rem; }

.steps { list-style: none; padding: 0; counter-reset: s; }
.steps li { counter-increment: s; position: relative; padding: 10px 0 10px 46px; margin-bottom: 4px; }
.steps li::before {
  content: counter(s); position: absolute; left: 0; top: 11px;
  width: 28px; height: 28px; border-radius: 50%; background: var(--panel2);
  border: 1px solid var(--line2); display: grid; place-items: center;
  font-family: var(--mono); font-size: .8rem; font-weight: 700; color: var(--acc);
}
.st-t { font-weight: 650; color: #fff; }
.st-d { color: var(--fg2); font-size: .93rem; }

.warnbox { background: rgba(251,191,36,.09); border: 1px solid rgba(251,191,36,.3);
  border-radius: 10px; padding: 14px 16px; color: #fde68a; margin: 14px 0; font-size: .93rem; }

.lessonfoot { margin-top: 34px; padding-top: 22px; border-top: 1px solid var(--line); }

/* ---------- tables ---------- */
.tbl { width: 100%; border-collapse: collapse; margin: 14px 0; font-size: .9rem; }
.tbl th { text-align: left; padding: 9px 12px; background: var(--panel2);
  color: var(--fg); font-weight: 650; border-bottom: 1px solid var(--line2); font-size: .84rem; }
.tbl td { padding: 9px 12px; border-bottom: 1px solid var(--line); color: var(--fg2); vertical-align: top; }
.tbl tr:hover td { background: rgba(56,189,248,.035); }
.tbl.compact { font-size: .84rem; }
.tbl.compact th, .tbl.compact td { padding: 6px 10px; }

.mat { border-collapse: collapse; font-family: var(--mono); }
.mat td { min-width: 40px; height: 32px; text-align: center; padding: 3px 8px;
  border: 1px solid var(--line2); background: var(--panel2); color: var(--fg); font-size: .84rem; }
.mat td.hi { background: rgba(244,114,182,.24); color: #fbcfe8; font-weight: 700; }
.matwrap { display: inline-block; margin: 6px 10px 6px 0; vertical-align: top; }
.matlabel { font-size: .76rem; color: var(--fg3); margin-bottom: 5px; font-family: var(--sans); }

/* ---------- widgets ---------- */
.widget { background: var(--panel); border: 1px solid var(--line); border-radius: 14px; padding: 20px; margin-top: 16px; }
.w { display: flex; flex-direction: column; gap: 14px; }
.w-info { font-size: .92rem; }
.w-extra { display: flex; flex-wrap: wrap; gap: 16px; align-items: flex-end; }
.tabs { display: flex; flex-wrap: wrap; gap: 6px; }
.tab { background: var(--panel2); border: 1px solid var(--line); color: var(--fg2);
  padding: 6px 12px; border-radius: 20px; cursor: pointer; font-family: inherit;
  font-size: .82rem; transition: all .15s; }
.tab:hover { border-color: var(--line2); color: var(--fg); }
.tab.on { background: var(--acc); border-color: var(--acc); color: #04121f; font-weight: 650; }
.row { display: flex; gap: 14px; align-items: center; flex-wrap: wrap; }
.chartbox { display: flex; flex-direction: column; gap: 6px; }
.chartlabel { font-size: .78rem; color: var(--fg3); letter-spacing: .06em;
  text-transform: uppercase; font-weight: 700; margin-top: 6px; }
.chart { width: 100%; max-width: 640px; border-radius: 8px; border: 1px solid var(--line); }
.gridcv { border: 1px solid var(--line2); border-radius: 8px; background: var(--bg2);
  touch-action: none; cursor: crosshair; display: block; }
.gridcv.small { display: block; }
.gridcv.tiny { display: inline-block; vertical-align: middle; }
.cols2 { display: grid; grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); gap: 18px; align-items: start; }
.cols3 { display: grid; grid-template-columns: repeat(auto-fit, minmax(230px, 1fr)); gap: 18px; align-items: start; }
.cols4 { display: grid; grid-template-columns: repeat(auto-fit, minmax(130px, 1fr)); gap: 14px; align-items: start; }

.sl { display: flex; flex-direction: column; gap: 5px; min-width: 190px; }
.sl label { display: flex; justify-content: space-between; font-size: .8rem; color: var(--fg2); gap: 12px; }
.sl-val { font-family: var(--mono); color: var(--acc); font-weight: 700; }
input[type=range] { -webkit-appearance: none; appearance: none; height: 5px; border-radius: 3px;
  background: var(--line2); outline: none; }
input[type=range]::-webkit-slider-thumb { -webkit-appearance: none; width: 17px; height: 17px;
  border-radius: 50%; background: var(--acc); cursor: pointer; border: 2px solid var(--bg); }
input[type=range]::-moz-range-thumb { width: 15px; height: 15px; border-radius: 50%;
  background: var(--acc); cursor: pointer; border: 2px solid var(--bg); }

.sel, .ta, .num {
  background: var(--panel2); border: 1px solid var(--line2); color: var(--fg);
  padding: 8px 11px; border-radius: 8px; font-family: inherit; font-size: .88rem;
}
.ta { width: 100%; font-family: var(--mono); font-size: .82rem; resize: vertical; }
.num { font-family: var(--mono); min-width: 200px; }
.num:focus, .ta:focus, .sel:focus { outline: none; border-color: var(--acc); }
.chk { display: flex; align-items: center; gap: 6px; font-size: .85rem; color: var(--fg2); }

.kv { display: flex; justify-content: space-between; gap: 16px; padding: 5px 0;
  border-bottom: 1px solid rgba(30,41,59,.6); font-size: .88rem; }
.kv span { color: var(--fg2); }
.kv b { font-family: var(--mono); }

.maskgrid { display: grid; grid-template-columns: repeat(auto-fill, minmax(360px, 1fr)); gap: 16px; }
.maskcard { background: var(--bg2); border: 1px solid var(--line); border-radius: 10px; padding: 12px; }
.mc-head { font-weight: 650; margin-bottom: 8px; color: #fff; }
.mc-row { display: flex; gap: 12px; flex-wrap: wrap; align-items: flex-start; margin-bottom: 8px; }
.mc-desc { font-size: .82rem; color: var(--fg2); margin-top: 8px; line-height: 1.5; }
.sebox { display: flex; align-items: center; gap: 14px; flex-wrap: wrap; }
.mini { width: 100%; height: 6px; background: var(--line); border-radius: 3px; overflow: hidden; }
.mini-fill { height: 100%; background: linear-gradient(90deg, var(--acc), var(--green)); }

/* ---------- quiz ---------- */
.quizcfg { background: var(--panel); border: 1px solid var(--line); border-radius: 12px; padding: 18px; margin-bottom: 18px; }
.cfgrow { display: flex; flex-wrap: wrap; gap: 18px; align-items: flex-end; }
.cfgrow label { display: flex; flex-direction: column; gap: 5px; font-size: .8rem; color: var(--fg2); }
.cfgrow label.chk { flex-direction: row; align-items: center; }
.startrow { margin-bottom: 22px; }
.qhost { margin-top: 10px; }

.quizq { background: var(--panel); border: 1px solid var(--line); border-radius: 14px; padding: 22px; }
.qhead { display: flex; gap: 14px; align-items: center; flex-wrap: wrap; margin-bottom: 14px; }
.qtag { background: var(--panel2); border: 1px solid var(--line2); color: var(--acc);
  padding: 3px 10px; border-radius: 14px; font-size: .74rem; font-weight: 700; }
.qnum { font-size: .82rem; color: var(--fg3); font-family: var(--mono); }
.qprog { margin-left: auto; }
.dots { display: inline-flex; gap: 4px; }
.dot { width: 8px; height: 8px; border-radius: 50%; background: var(--line2); display: inline-block; }
.dot.cur { background: var(--acc); transform: scale(1.35); }
.dot.good { background: var(--green); }
.dot.bad { background: var(--red); }

.qtext { font-size: 1rem; line-height: 1.7; margin-bottom: 16px; color: #dbe4f0; }
.qtext code { font-size: .9em; }
.ansbox { display: flex; flex-direction: column; gap: 8px; margin-bottom: 14px; }
.opt { background: var(--panel2); border: 1px solid var(--line2); color: var(--fg);
  padding: 11px 15px; border-radius: 9px; cursor: pointer; text-align: left;
  font-family: inherit; font-size: .92rem; transition: all .14s; }
.opt:hover { border-color: var(--acc); background: #16233d; }
.opt.sel { border-color: var(--acc); background: rgba(56,189,248,.12); }
.opt.dim { opacity: .45; }
.numrow { display: flex; gap: 10px; flex-wrap: wrap; }

.verdict { font-weight: 750; font-size: 1rem; margin-bottom: 8px; }
.verdict.good { color: var(--green); }
.verdict.bad { color: var(--red); }
.solution { background: var(--bg2); border: 1px solid var(--line); border-left: 3px solid var(--acc);
  border-radius: 0 8px 8px 0; padding: 13px 16px; font-size: .9rem; color: var(--fg2); line-height: 1.65; }
.solution b { color: #fff; }
.qnav { display: flex; gap: 10px; margin-top: 18px; flex-wrap: wrap; }

.summary { background: var(--panel); border: 1px solid var(--line); border-radius: 14px; padding: 26px; }
.summary h2 { margin-bottom: 4px; }
.bigscore { font-size: 3.4rem; font-weight: 800; letter-spacing: -.04em;
  background: linear-gradient(135deg, var(--acc), var(--green));
  -webkit-background-clip: text; background-clip: text; color: transparent; margin: 8px 0 2px; }
.reviewlist { list-style: none; padding: 0; }
.reviewlist li { background: var(--bg2); border: 1px solid var(--line); border-radius: 10px;
  padding: 13px 15px; margin-bottom: 10px; font-size: .9rem; color: var(--fg2); }

/* ---------- mock ---------- */
.mockinfo { background: var(--panel); border: 1px solid var(--line); border-radius: 12px; padding: 18px; margin-bottom: 16px; }
.mockhead { display: flex; justify-content: space-between; align-items: center;
  margin-bottom: 16px; gap: 14px; flex-wrap: wrap; }
.mh-l { display: flex; flex-direction: column; gap: 4px; }
.timer { font-family: var(--mono); font-size: 1.5rem; font-weight: 700; color: var(--acc);
  background: var(--panel); border: 1px solid var(--line2); padding: 5px 14px; border-radius: 9px; }

/* ---------- reference sheet ---------- */
.refcard { background: var(--panel); border: 1px solid var(--line); border-radius: 14px;
  padding: 26px 30px; font-size: .86rem; line-height: 1.7; }
.refcard h3 { margin-top: 22px; color: var(--acc); border-bottom: 1px solid var(--line2); padding-bottom: 5px; }
.refcard h3:first-child { margin-top: 0; }
.refcard pre { white-space: pre-wrap; background: transparent; border: none; padding: 0; font-size: .84rem; line-height: 1.65; }
.refcard code { background: transparent; padding: 0; color: #7dd3fc; }

/* ---------- mobile ---------- */
@media (max-width: 860px) {
  .shell { flex-direction: column; }
  #sidebar { width: 100%; flex: none; height: auto; position: static; border-right: none;
    border-bottom: 1px solid var(--line); padding: 14px; }
  .main { padding: 20px 16px 70px; }
  .nav { flex-direction: row; flex-wrap: wrap; gap: 6px; }
  .navbtn { padding: 7px 11px; }
  .nb-s { display: none; }
  .tutnav { flex-direction: row; flex-wrap: wrap; }
  .tnav { width: auto; }
  .tnav-s { display: none; }
  .tnav-d { position: static; display: block; }
  h1 { font-size: 1.45rem; }
  .widget { padding: 14px; }
  .cols2, .cols3, .cols4 { grid-template-columns: 1fr; }
  .lgrid { grid-template-columns: 1fr; }
  .refcard { padding: 16px; font-size: .78rem; }
  .bigscore { font-size: 2.6rem; }
}

@media print {
  #sidebar, .btn, .qnav { display: none !important; }
  body { background: #fff; color: #000; }
  .refcard { border: none; padding: 0; }
  .refcard code, .refcard pre { color: #000; }
}