:root{
  --paper:#F6F8FC; --card:#FFFFFF; --ink:#172342; --soft:#55607A; --faint:#8791A7;
  --blue:#2447B8; --on-blue:#FFFFFF; --blue-soft:#E7ECFA; --line:#DCE2EE; --grid:rgba(36,71,184,.07);
  --hl-paper:#FFE45C; --hl-concept:#BFD3FF; --hl-design:#B8EBC9; --hl-trend:#FFC7DA;
  --red:#C8372D; --red-soft:#FBE8E6; --green:#1E7B4F; --green-soft:#E3F3EA;
  --serif:"Newsreader",Georgia,"Times New Roman",serif;
  --sans:"Manrope",system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;
  --mono:ui-monospace,"SF Mono",Menlo,Consolas,monospace;
  color-scheme:light;
  box-sizing:border-box;
  padding-top:env(safe-area-inset-top,0px);
  padding-bottom:env(safe-area-inset-bottom,0px);
}
@media (prefers-color-scheme:dark){
  :root:not([data-theme="light"]){
    --paper:#0F131C; --card:#161C29; --ink:#E7EBF5; --soft:#A7B0C5; --faint:#78829A;
    --blue:#8EA7FF; --on-blue:#0E1426; --blue-soft:#1C2540; --line:#283148; --grid:rgba(142,167,255,.05);
    --hl-paper:rgba(255,214,64,.38); --hl-concept:rgba(120,160,255,.38); --hl-design:rgba(90,210,140,.34); --hl-trend:rgba(255,120,170,.34);
    --red:#FF7B6F; --red-soft:#3A1E1E; --green:#63D69C; --green-soft:#17301F;
    color-scheme:dark;
  }
}
:root[data-theme="dark"]{
  --paper:#0F131C; --card:#161C29; --ink:#E7EBF5; --soft:#A7B0C5; --faint:#78829A;
  --blue:#8EA7FF; --on-blue:#0E1426; --blue-soft:#1C2540; --line:#283148; --grid:rgba(142,167,255,.05);
  --hl-paper:rgba(255,214,64,.38); --hl-concept:rgba(120,160,255,.38); --hl-design:rgba(90,210,140,.34); --hl-trend:rgba(255,120,170,.34);
  --red:#FF7B6F; --red-soft:#3A1E1E; --green:#63D69C; --green-soft:#17301F;
  color-scheme:dark;
}
*,*::before,*::after{box-sizing:inherit}
html{scroll-padding-top:env(safe-area-inset-top,0px)}
body{
  margin:0; color:var(--ink); background-color:var(--paper);
  background-image:linear-gradient(var(--grid) 1px,transparent 1px),linear-gradient(90deg,var(--grid) 1px,transparent 1px);
  background-size:24px 24px;
  font:16px/1.55 var(--sans);
  -webkit-font-smoothing:antialiased;
}
main{max-width:720px;margin:0 auto;padding:22px 18px 120px}
button,input,select,textarea{font:inherit;color:inherit}
:focus-visible{outline:2px solid var(--blue);outline-offset:2px;border-radius:6px}
a{color:var(--blue)}
img{max-width:100%}

h1.page{font:500 2rem/1.15 var(--serif);letter-spacing:-.01em;margin:.2rem 0 .5rem}
.date{color:var(--soft);font-size:.9rem;margin:0}
.lead{color:var(--soft);margin:0 0 1.4rem;max-width:36em}
h2.sec{font:600 1.05rem/1.3 var(--sans);margin:2.2rem 0 .4rem}
.hint{color:var(--soft);font-size:.92rem;margin:.2rem 0 .8rem}
.small{font-size:.85rem}

.btn{appearance:none;border:0;background:var(--blue);color:var(--on-blue);font-weight:600;padding:.72rem 1.1rem;border-radius:10px;cursor:pointer;min-height:44px}
.btn:disabled{opacity:.5;cursor:not-allowed}
.btn.ghost{background:transparent;color:var(--blue);box-shadow:inset 0 0 0 1.5px var(--blue)}
.btn.quiet{background:var(--blue-soft);color:var(--blue)}
.link{appearance:none;border:0;background:none;color:var(--blue);padding:.4rem 0;cursor:pointer;font-weight:600}
.link.danger{color:var(--red)}
.row{display:flex;flex-wrap:wrap;gap:.6rem;align-items:center;margin:.8rem 0}

.status{color:var(--soft);font-size:.92rem;margin:.4rem 0;min-height:1.2em}
.status.err{color:var(--red)}
.pulse{display:inline-block;width:.55em;height:.55em;border-radius:50%;background:var(--blue);margin-right:.5em;vertical-align:middle;animation:pulse 1.1s ease-in-out infinite}
@keyframes pulse{0%,100%{opacity:.25}50%{opacity:1}}
@media (prefers-reduced-motion:reduce){.pulse{animation:none;opacity:.7}}

.focus{border-left:3px solid var(--blue);padding:.2rem 0 .2rem .9rem;margin:0 0 1rem}
.focus-label{font-size:.85rem;color:var(--soft);font-weight:600}
.focus p{margin:.15rem 0 0;font:400 1.15rem/1.45 var(--serif)}

.list{display:grid;gap:.7rem}
.item{display:block;width:100%;text-align:left;background:var(--card);border:1px solid var(--line);border-radius:12px;padding:.9rem 1rem;cursor:pointer}
.item:hover{border-color:var(--blue)}
.item-top{display:flex;gap:.7rem;align-items:baseline;flex-wrap:wrap;font-size:.8rem;color:var(--soft)}
.item-title{font:500 1.18rem/1.3 var(--serif);margin:.35rem 0 .15rem;color:var(--ink)}
.item-detail{font-size:.85rem;color:var(--faint);margin:0}
.item-why{font-size:.93rem;color:var(--soft);margin:.4rem 0 0}
.item-note{font-size:.85rem;color:var(--red);margin:.4rem 0 0;font-weight:600}
.item.done{border-style:dashed}
.done-mark{color:var(--green);font-weight:700}

.tag{font-weight:700;font-size:.78rem;color:var(--ink);padding:0 .25em;
  background:linear-gradient(transparent 42%,var(--hl) 42%,var(--hl) 92%,transparent 92%)}
.k-paper{--hl:var(--hl-paper)} .k-concept{--hl:var(--hl-concept)} .k-system-design{--hl:var(--hl-design)} .k-trend{--hl:var(--hl-trend)}

.ask{display:flex;gap:.5rem;flex-wrap:wrap;margin:0 0 .8rem}
.field{flex:1 1 220px;min-height:46px;padding:.65rem .8rem;border:1.5px solid var(--line);border-radius:10px;background:var(--card)}
.field:focus{border-color:var(--blue);outline:none}
textarea.field{min-height:90px;resize:vertical;width:100%}
select.field{width:100%}
.chips{display:flex;flex-wrap:wrap;gap:.45rem;margin:.3rem 0 1rem}
.chip{appearance:none;border:1.5px solid var(--line);background:var(--card);border-radius:999px;padding:.4rem .8rem;font-size:.88rem;cursor:pointer;min-height:36px}
.chip[aria-pressed="true"]{border-color:var(--blue);background:var(--blue-soft);color:var(--blue);font-weight:600}

details.path{background:var(--card);border:1px solid var(--line);border-radius:12px;margin:.7rem 0;padding:.2rem 1rem}
details.path summary{cursor:pointer;padding:.7rem 0;display:flex;justify-content:space-between;gap:1rem;align-items:baseline;list-style:none}
details.path summary::-webkit-details-marker{display:none}
.path-title{font:500 1.2rem/1.3 var(--serif)}
.path-prog{font-size:.82rem;color:var(--soft);white-space:nowrap}
ol.steps{list-style:none;counter-reset:s;padding:0;margin:.4rem 0 .6rem;display:grid;gap:.6rem}
ol.steps>li{counter-increment:s;display:grid;grid-template-columns:2rem 1fr;align-items:start}
ol.steps>li::before{content:counter(s);font:500 1.3rem/1 var(--serif);color:var(--blue);padding-top:1rem}

.back{margin:0 0 .6rem}
.learn-head .meta-row{display:flex;flex-wrap:wrap;gap:.9rem;font-size:.85rem;color:var(--soft);margin:.3rem 0 .6rem}
.src-links{display:flex;flex-wrap:wrap;gap:1rem;font-size:.9rem;font-weight:600;margin:.2rem 0 1rem}
.reading{font:400 1.12rem/1.68 var(--serif);max-width:40em}
.reading h2,.reading h3,.reading h4{font-family:var(--sans);font-weight:700;line-height:1.3;margin:1.8rem 0 .5rem}
.reading h2{font-size:1.08rem;color:var(--blue)}
.reading h3{font-size:1rem}
.reading h4{font-size:.95rem}
.reading p{margin:.6rem 0}
.reading ul,.reading ol{padding-left:1.3rem;margin:.5rem 0}
.reading li{margin:.3rem 0}
.reading strong{font-weight:600}
.reading code{font-family:var(--mono);font-size:.82em;background:var(--blue-soft);padding:.08em .3em;border-radius:4px}
.reading pre{background:var(--blue-soft);border-radius:10px;padding:.9rem 1rem;overflow-x:auto;line-height:1.45}
.reading pre code{background:none;padding:0;font-size:.82rem;white-space:pre}
.reading blockquote{margin:.8rem 0;padding-left:1rem;border-left:3px solid var(--line);color:var(--soft)}
.reading hr{border:0;border-top:1px solid var(--line);margin:1.5rem 0}
.scroll{overflow-x:auto;margin:.8rem 0}
.reading table{border-collapse:collapse;font:400 .9rem/1.45 var(--sans);min-width:100%}
.reading th,.reading td{border:1px solid var(--line);padding:.45rem .6rem;text-align:left;vertical-align:top}
.reading th{background:var(--blue-soft)}
.actions{border-top:1px solid var(--line);margin-top:1.6rem;padding-top:1rem}

.quiz fieldset{border:1px solid var(--line);background:var(--card);border-radius:12px;padding:.8rem 1rem 1rem;margin:0 0 .8rem}
.quiz legend{font-weight:600;padding:0 .3rem;max-width:100%}
.opt{display:flex;gap:.6rem;align-items:flex-start;padding:.45rem .5rem;border-radius:8px;cursor:pointer}
.opt input{margin-top:.3rem;accent-color:var(--blue)}
.opt.right{background:var(--green-soft)}
.opt.wrong{background:var(--red-soft)}
.why{font-size:.92rem;color:var(--soft);margin:.5rem 0 0}
.grade-wrap{display:flex;gap:1rem;align-items:center;margin:1rem 0}
.grade{width:86px;height:86px;flex:none;display:grid;place-items:center;color:var(--red);
  border:3px solid var(--red);border-radius:47% 53% 50% 50% / 53% 47% 53% 47%;
  font:600 1.7rem/1 var(--serif);transform:rotate(-8deg)}
.grade.sm{width:52px;height:52px;font-size:1.05rem;border-width:2px}

.chat{margin-top:1.6rem}
.bubble{padding:.7rem .9rem;border-radius:12px;margin:.5rem 0;max-width:40em}
.bubble.me{background:var(--blue-soft);margin-left:auto;font-size:.95rem}
.bubble.ai{background:var(--card);border:1px solid var(--line)}
.bubble.ai.reading{font-size:1.02rem}

.stats{display:grid;grid-template-columns:repeat(3,1fr);gap:.6rem}
.stat{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:.8rem}
.stat b{display:block;font:500 1.8rem/1.1 var(--serif)}
.stat span{font-size:.82rem;color:var(--soft)}
.area-row{display:grid;grid-template-columns:minmax(0,1fr) auto;gap:.2rem .8rem;padding:.55rem 0;border-bottom:1px solid var(--line);font-size:.92rem}
.bar{grid-column:1/-1;height:6px;background:var(--blue-soft);border-radius:3px;overflow:hidden}
.bar i{display:block;height:100%;background:var(--blue)}
.area-num{color:var(--soft);font-size:.85rem;white-space:nowrap}
.hist{display:flex;gap:.9rem;align-items:center;padding:.5rem 0;border-bottom:1px solid var(--line)}
.hist p{margin:0}

.term{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:.8rem 1rem;margin:.6rem 0}
.term h3{margin:0;font:600 1.1rem/1.3 var(--serif)}
.term p{margin:.3rem 0 0;font-size:.95rem}
.term .ex{color:var(--soft);font-style:italic}
.term .from{color:var(--faint);font-size:.8rem}

.form-grid{display:grid;gap:1.1rem}
.form-grid label{font-weight:600;font-size:.92rem;display:block;margin-bottom:.35rem}

nav.tabs{position:fixed;left:0;right:0;bottom:0;z-index:5;background:var(--card);border-top:1px solid var(--line);
  padding-bottom:env(safe-area-inset-bottom,0px)}
nav.tabs .in{max-width:720px;margin:0 auto;display:grid;grid-template-columns:repeat(5,1fr)}
nav.tabs button{appearance:none;border:0;background:none;padding:.55rem 0 .6rem;display:flex;flex-direction:column;align-items:center;gap:.15rem;font-size:.75rem;font-weight:600;color:var(--faint);cursor:pointer;min-height:54px}
nav.tabs button[aria-current="page"]{color:var(--blue)}
nav.tabs svg{width:22px;height:22px}
.hidden{display:none!important}

.toast{position:fixed;left:50%;transform:translateX(-50%);bottom:calc(76px + env(safe-area-inset-bottom,0px));z-index:9;
  background:var(--ink);color:var(--paper);padding:.6rem 1rem;border-radius:10px;font-size:.9rem;max-width:calc(100% - 32px)}
.auth{max-width:420px;margin:8vh auto 0}
.auth .field{width:100%;margin:.35rem 0}
.brand{display:flex;gap:.7rem;align-items:center;margin-bottom:1rem}
.brand img{width:44px;height:44px;border-radius:12px}
.brand b{font:600 1.3rem/1 var(--serif)}
.paper{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:.9rem 1rem}
.paper h3{font:500 1.15rem/1.3 var(--serif);margin:.35rem 0 .2rem}
.paper .by{font-size:.82rem;color:var(--faint);margin:0}
.paper .simple{margin:.5rem 0 0;font-size:.95rem}
.paper .why{margin:.4rem 0 0}
.paper .row{margin:.6rem 0 0}
.day-h{font-size:.9rem;color:var(--soft);font-weight:700;margin:1.6rem 0 .5rem}
.setting{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:.9rem 1rem;margin:.6rem 0}
.setting h3{margin:0 0 .2rem;font-size:1rem}
.setting p{margin:.2rem 0}

/* ---------- curriculum path ---------- */
.bar.big{grid-column:auto;height:10px;border-radius:5px;margin:.2rem 0 .4rem}
.step{display:block;width:100%;text-align:left;background:var(--card);border:1px solid var(--line);
  border-radius:12px;padding:.9rem 1rem;cursor:pointer;margin:0 0 .6rem;position:relative}
.step:hover:not(:disabled){border-color:var(--blue)}
.step:disabled{cursor:not-allowed;opacity:.62}
.step-top{display:flex;gap:.7rem;align-items:baseline;flex-wrap:wrap;font-size:.8rem;color:var(--soft)}
.step.ready{border-left:4px solid var(--blue)}
.step.learning{border-left:4px solid var(--hl-paper)}
.step.mastered{border-left:4px solid var(--green)}
.step.mastered .item-title::after{content:" ✓";color:var(--green)}
.step.locked{border-left:4px solid var(--line);background:transparent}
.step.due{box-shadow:0 0 0 2px var(--blue-soft)}
.chip.on{border-color:var(--blue);background:var(--blue-soft);color:var(--blue);font-weight:600}
textarea.field.tall{min-height:180px;font-family:var(--mono);font-size:.88rem;line-height:1.5}
.steps li.right{color:var(--green)}
.steps li.wrong{color:var(--red)}