/* ===========================================================
   HW Design — Karteikarten
   Palette taken from the subject itself: soldermask green board,
   ENIG gold pads, copper traces, and #C0C0C0 — the exact grey the
   schematic captures were drawn on, so the images sit flush on the card.
   =========================================================== */

@font-face{font-family:Chivo;src:url(vendor/fonts/chivo-latin-900-normal.woff2) format('woff2');font-weight:900;font-display:swap}
@font-face{font-family:Chivo;src:url(vendor/fonts/chivo-latin-700-normal.woff2) format('woff2');font-weight:700;font-display:swap}
@font-face{font-family:PlexMono;src:url(vendor/fonts/ibm-plex-mono-latin-400-normal.woff2) format('woff2');font-weight:400;font-display:swap}
@font-face{font-family:PlexMono;src:url(vendor/fonts/ibm-plex-mono-latin-600-normal.woff2) format('woff2');font-weight:600;font-display:swap}

:root{
  --board:#0a2a22;
  --board-2:#0e372c;
  --deep:#051712;
  --line:rgba(217,164,65,.20);
  --silk:#edf2ed;
  --silk-dim:rgba(237,242,237,.58);
  --gold:#d9a441;
  --copper:#c0703c;
  --slate:#c0c0c0;      /* LTspice canvas grey */
  --ink:#0e1f19;
  --mono:PlexMono,ui-monospace,"SF Mono",Menlo,Consolas,monospace;
  --disp:Chivo,"Arial Black","Helvetica Neue",system-ui,sans-serif;
  --pad:clamp(14px,3vw,28px);
}

*{box-sizing:border-box}
/* the whole layout holds a fixed measure; on ultrawide the board shows around it */
.top,.rail,.view,.foot{width:100%;max-width:1280px;margin-left:auto;margin-right:auto}
html,body{margin:0}
body{
  min-height:100vh;
  background:
    radial-gradient(circle at 1px 1px,rgba(237,242,237,.055) 1px,transparent 0) 0 0/22px 22px,
    linear-gradient(160deg,var(--board) 0%,var(--deep) 100%) fixed;
  color:var(--silk);
  font-family:var(--mono);
  font-size:15px;
  line-height:1.5;
  -webkit-font-smoothing:antialiased;
  display:flex;flex-direction:column;
}
button,select,input{font:inherit;color:inherit}
:focus-visible{outline:2px solid var(--gold);outline-offset:3px}

/* ---------- header ---------- */
.top{
  display:flex;align-items:center;justify-content:space-between;gap:16px;flex-wrap:wrap;
  padding:18px var(--pad) 14px;
}
.brand{display:flex;align-items:center;gap:14px}
.chip{width:38px;height:31px;color:var(--gold);flex:none}
.brand-text h1{
  font-family:var(--disp);font-weight:900;font-size:clamp(19px,2.4vw,25px);
  letter-spacing:-.02em;text-transform:uppercase;margin:0;line-height:1;
}
.eyebrow{
  margin:5px 0 0;font-size:11px;letter-spacing:.16em;text-transform:uppercase;
  color:var(--silk-dim);
}
.views{display:flex;gap:2px;background:rgba(0,0,0,.28);padding:3px;border-radius:2px;border:1px solid var(--line)}
.tab{
  background:none;border:0;padding:7px 15px;cursor:pointer;border-radius:1px;
  font-size:12px;letter-spacing:.12em;text-transform:uppercase;color:var(--silk-dim);
}
.tab:hover{color:var(--silk)}
.tab.is-on{background:var(--gold);color:#20160a;font-weight:600}

/* ---------- signature: the board rail ---------- */
.rail-wrap{padding:0 var(--pad) 4px;overflow-x:auto;scrollbar-width:thin}
.rail{
  position:relative;display:flex;align-items:center;gap:2px;
  min-width:640px;padding:14px 0 16px;
}
.rail::before{           /* the copper trace the pads sit on */
  content:"";position:absolute;left:0;right:0;top:50%;height:2px;
  background:linear-gradient(90deg,transparent,var(--copper) 3%,var(--copper) 97%,transparent);
  opacity:.45;
}
.pad{
  position:relative;flex:1 1 0;height:11px;min-width:5px;border:0;padding:0;
  background:none;cursor:pointer;
}
.pad::after{
  content:"";position:absolute;inset:0;margin:auto;
  width:9px;height:9px;border-radius:50%;
  border:1.5px solid rgba(217,164,65,.45);background:var(--deep);
  transition:transform .18s ease,background .18s ease,border-color .18s ease;
}
.pad:hover::after{border-color:var(--silk);transform:scale(1.25)}
.pad[data-s="got"]::after{background:var(--gold);border-color:var(--gold)}
.pad[data-s="again"]::after{background:var(--copper);border-color:var(--copper)}
.pad[data-flag="1"]::after{box-shadow:0 0 0 2px rgba(237,242,237,.75)}
.pad.is-here::after{
  transform:scale(1.7);background:var(--silk);border-color:var(--silk);
  box-shadow:0 0 0 3px rgba(237,242,237,.18);
}

/* ---------- shared controls ---------- */
main{flex:1;padding:0 var(--pad) 26px;display:flex;flex-direction:column}
.view{display:none;flex:1;flex-direction:column}
.view.is-on{display:flex}

.bar{
  display:flex;flex-wrap:wrap;gap:10px 18px;align-items:flex-end;justify-content:space-between;
  padding:10px 0 16px;border-bottom:1px solid var(--line);margin-bottom:20px;
}
.bar-group{display:flex;gap:10px;align-items:flex-end;flex-wrap:wrap}
.bar-group.grow{flex:1}
.sel{display:flex;flex-direction:column;gap:4px}
.lab{font-size:10px;letter-spacing:.16em;text-transform:uppercase;color:var(--silk-dim)}
select,.search{
  background:rgba(0,0,0,.3);border:1px solid var(--line);border-radius:2px;
  padding:7px 10px;font-size:13px;
}
select{cursor:pointer;min-width:150px}
.search{width:100%;max-width:520px}
option{background:#0d2b23}

.btn{
  background:var(--gold);color:#20160a;border:1px solid var(--gold);border-radius:2px;
  padding:9px 16px;cursor:pointer;font-size:12px;letter-spacing:.1em;text-transform:uppercase;
  font-weight:600;display:inline-flex;align-items:center;gap:8px;
  transition:filter .15s ease,background .15s ease;
}
.btn b{
  font-weight:400;font-size:10px;opacity:.65;border:1px solid currentColor;
  border-radius:2px;padding:1px 5px;letter-spacing:0;text-transform:none;
}
.btn:hover{filter:brightness(1.1)}
.btn.ghost{background:none;color:var(--silk-dim);border-color:var(--line)}
.btn.ghost:hover{color:var(--silk);border-color:var(--silk)}
.btn.ghost.danger:hover{color:var(--copper);border-color:var(--copper)}
.btn.again{background:var(--copper);border-color:var(--copper);color:#1c0e06}
.btn.flip{background:none;color:var(--silk);border-color:var(--silk)}
.btn.flag[aria-pressed=true]{background:var(--silk);color:var(--ink);border-color:var(--silk)}

/* ---------- the card ---------- */
.stage{display:flex;align-items:center;gap:10px;flex:1}
.card-slot{flex:1;perspective:2200px;min-width:0}
.nav{
  background:none;border:1px solid var(--line);color:var(--silk-dim);
  width:38px;height:74px;border-radius:2px;cursor:pointer;font-size:26px;line-height:1;flex:none;
}
.nav:hover{color:var(--silk);border-color:var(--silk)}

.card{
  position:relative;width:100%;min-height:clamp(340px,calc(100vh - 400px),560px);
  transform-style:preserve-3d;transition:transform .5s cubic-bezier(.2,.7,.2,1);
  cursor:pointer;
}
.card.flipped{transform:rotateY(180deg)}
.face{
  position:absolute;inset:0;backface-visibility:hidden;-webkit-backface-visibility:hidden;
  border-radius:3px;overflow:auto;padding:26px 30px 40px;
  display:flex;flex-direction:column;align-items:center;justify-content:center;gap:14px;
}
.face-a{background:var(--slate);color:var(--ink);box-shadow:0 18px 40px rgba(0,0,0,.42)}
.face-b{
  transform:rotateY(180deg);
  background:var(--board-2);color:var(--silk);
  border:1px solid var(--line);box-shadow:0 18px 40px rgba(0,0,0,.42);
}
/* the schematic side is grey; the answer side is the board */
.face.is-schematic{background:var(--slate);color:var(--ink);border:0}
.face.is-answer{background:var(--board-2);color:var(--silk);border:1px solid var(--line)}

.ref{
  position:absolute;top:12px;left:16px;font-size:10px;letter-spacing:.18em;
  text-transform:uppercase;opacity:.45;
}
.hint{
  position:absolute;bottom:12px;left:0;right:0;text-align:center;
  font-size:10px;letter-spacing:.18em;text-transform:uppercase;opacity:.35;
}

.answer{
  font-family:var(--disp);font-weight:900;text-transform:uppercase;letter-spacing:-.015em;
  font-size:clamp(24px,4.4vw,46px);line-height:1.02;text-align:center;margin:0;
  max-width:20ch;
}
.answer.long{font-size:clamp(19px,2.6vw,31px);max-width:24ch;line-height:1.08}
.answer-group{
  font-size:11px;letter-spacing:.2em;text-transform:uppercase;color:var(--gold);
  border-top:1px solid var(--line);padding-top:12px;margin-top:4px;
}

/* card body content coming out of the LaTeX */
.body{display:flex;flex-direction:column;align-items:center;gap:10px;width:100%}
.body p,.body .row{margin:0;text-align:center;width:100%}
.body .row{display:flex;flex-wrap:wrap;gap:12px;align-items:center;justify-content:center}
.body img.sch{
  width:var(--w,80%);max-width:100%;height:auto;image-rendering:auto;display:block;
  max-height:min(38vh,380px);object-fit:contain;
}
/* two-diagram cards (charge/discharge, rectifier + plot) share the height budget */
.body .row:has(img.sch + img.sch) img.sch{max-height:min(26vh,250px)}
.face-b .body img.sch,.face.is-answer .body img.sch{border-radius:2px}
.math{display:inline-block;max-width:100%;overflow-x:auto;overflow-y:hidden;vertical-align:middle}
.katex{font-size:1.02em}
.face.is-answer .katex,.face-b .katex{color:var(--silk)}
table.tt{border-collapse:collapse;margin:0 auto;font-size:13px}
table.tt th,table.tt td{border:1px solid rgba(14,31,25,.5);padding:3px 13px;text-align:center}
table.tt th{font-weight:600}
.face.is-answer table.tt th,.face.is-answer table.tt td{border-color:var(--line)}

.actions{display:flex;gap:10px;justify-content:center;flex-wrap:wrap;padding:20px 0 6px}
.status{text-align:center;font-size:12px;color:var(--silk-dim);margin:0;letter-spacing:.04em}
.status b{color:var(--gold);font-weight:400}

/* ---------- quiz ---------- */
.quiz-panel{max-width:900px;margin:0 auto;width:100%}
.quiz-prompt{
  background:var(--slate);color:var(--ink);border-radius:3px;padding:26px 22px;
  display:flex;flex-direction:column;align-items:center;gap:12px;
  min-height:200px;max-height:46vh;overflow:auto;
  justify-content:center;box-shadow:0 14px 32px rgba(0,0,0,.38);position:relative;
}
.quiz-prompt .body img.sch{max-height:34vh;object-fit:contain}
.quiz-options{display:grid;grid-template-columns:1fr 1fr;gap:10px;margin-top:18px}
.opt{
  text-align:left;background:rgba(0,0,0,.24);border:1px solid var(--line);border-radius:2px;
  padding:14px 16px;cursor:pointer;font-size:14px;line-height:1.3;
  display:flex;gap:12px;align-items:baseline;
}
.opt span{font-size:11px;color:var(--gold);letter-spacing:.1em}
.opt:hover:not(:disabled){border-color:var(--silk)}
.opt.right{background:rgba(217,164,65,.16);border-color:var(--gold)}
.opt.wrong{background:rgba(192,112,60,.16);border-color:var(--copper)}
.opt:disabled{cursor:default}
.score{font-size:12px;letter-spacing:.1em;text-transform:uppercase;color:var(--silk-dim);align-self:center}

/* ---------- browse ---------- */
.grid{
  display:grid;gap:12px;
  grid-template-columns:repeat(auto-fill,minmax(210px,1fr));
}
.tile{
  background:rgba(0,0,0,.22);border:1px solid var(--line);border-radius:3px;
  padding:0 0 12px;cursor:pointer;text-align:left;overflow:hidden;
  display:flex;flex-direction:column;gap:10px;
}
.tile:hover{border-color:var(--silk)}
.tile .thumb{
  background:var(--slate);height:118px;display:flex;align-items:center;justify-content:center;
  padding:8px;
}
.tile .thumb img{max-width:100%;max-height:100%;object-fit:contain}
.tile .thumb.empty{font-size:11px;color:rgba(14,31,25,.5);letter-spacing:.12em;text-transform:uppercase}
.tile h3{
  font-family:var(--disp);font-weight:700;text-transform:uppercase;font-size:13px;
  letter-spacing:-.005em;margin:0;padding:0 12px;line-height:1.15;
}
.tile .meta{
  font-size:10px;letter-spacing:.14em;text-transform:uppercase;color:var(--silk-dim);
  padding:0 12px;display:flex;justify-content:space-between;gap:8px;
}
.tile[data-s="got"]{border-color:rgba(217,164,65,.55)}
.tile[data-s="got"] .meta em{color:var(--gold);font-style:normal}
.tile[data-s="again"] .meta em{color:var(--copper);font-style:normal}
.empty-note{color:var(--silk-dim);text-align:center;padding:50px 0}

/* ---------- footer ---------- */
.foot{
  border-top:1px solid var(--line);padding:14px var(--pad);
  display:flex;justify-content:space-between;gap:14px;flex-wrap:wrap;
  font-size:11px;color:var(--silk-dim);letter-spacing:.04em;
}
.foot code{font-size:11px;color:var(--gold)}
.keys{opacity:.8}

@media (max-width:720px){
  .nav{display:none}
  .quiz-options{grid-template-columns:1fr}
  .face{padding:30px 16px 42px}
  .card{min-height:min(58vh,460px)}
  .foot .keys{display:none}
  .btn b{display:none}
  .actions{gap:8px}
  select{min-width:120px}
}

/* phones — portrait */
@media (max-width:480px){
  :root{--pad:14px}

  /* header stacks: brand top, tabs below filling full width */
  .top{
    flex-direction:column;align-items:flex-start;gap:10px;
    padding:12px var(--pad) 10px;
  }
  .chip{width:28px;height:22px}
  .brand-text h1{font-size:18px}
  .eyebrow{display:none}
  .views{width:100%}
  .tab{flex:1;text-align:center;padding:7px 4px;font-size:11px}

  /* bar controls stack vertically */
  .bar{flex-direction:column;align-items:stretch;gap:10px;padding:8px 0 14px;margin-bottom:14px}
  .bar-group{flex-wrap:wrap;gap:8px}
  .bar-group.grow{flex:none;width:100%}
  .sel{width:100%}
  select{min-width:0;width:100%}
  .search{max-width:100%}

  /* card */
  .card{min-height:min(48vh,360px)}

  /* action buttons — bigger touch targets, no keyboard labels */
  .actions{padding:12px 0 4px;gap:6px}
  .btn{padding:11px 10px;font-size:11px;gap:5px}

  /* quiz */
  .quiz-panel{margin:0}
  .quiz-prompt{min-height:140px;max-height:36vh;padding:16px 14px}

  /* footer: drop the long source attribution, keep it short */
  .foot{padding:10px var(--pad);font-size:10px}
  .foot span:first-child{display:none}

  .status{font-size:11px}
}

/* very small phones (320–360 px) */
@media (max-width:360px){
  .tab{font-size:10px;letter-spacing:.08em}
  .btn{padding:10px 7px;font-size:10px}
  .card{min-height:min(44vh,300px)}
  .quiz-prompt{max-height:32vh}
}

@media (prefers-reduced-motion:reduce){
  .card{transition:none}
  .pad::after{transition:none}
}