/* ===========================================================
   재료역학 개념 앱 — 공용 디자인 시스템
   구조공학 관용: 압축=청색 / 인장=적갈색, 제도 그리드
   =========================================================== */
:root{
  --ground:#F4F6F8; --surface:#FFFFFF; --surface-2:#EBEFF3;
  --ink:#16202B; --ink-soft:#4C5A69; --ink-faint:#77848F;
  --rule:#D3DBE3; --rule-soft:#E4EAEF;
  --comp:#1F5C8B; --comp-wash:#E7EFF6; --comp-soft:#8FB6D2;
  --tens:#B24328; --tens-wash:#FAEAE5; --tens-soft:#D99C89;
  --neut:#5C7C6E; --neut-wash:#E7EFEB;
  --on-accent:#FFFFFF;
  --chip:#DDE4EB;
  --shadow:0 1px 2px rgba(22,32,43,.06), 0 8px 24px -18px rgba(22,32,43,.5);
  --grid-line:#E4EAEF;
}

/* --- 종이 테마 : 장시간 읽기·강의실 프로젝터용 --- */
:root[data-theme="paper"]{
  --ground:#F2EDE3; --surface:#FBF8F2; --surface-2:#EAE3D6;
  --ink:#2B2620; --ink-soft:#5C544A; --ink-faint:#8A8074;
  --rule:#D8CFBF; --rule-soft:#E6DFD2;
  --comp:#1D5A7A; --comp-wash:#E2ECF1; --comp-soft:#8CB4C8;
  --tens:#A8442A; --tens-wash:#F5E6DF; --tens-soft:#D19C86;
  --neut:#4F7255; --neut-wash:#E5EDE4;
  --on-accent:#FBF8F2;
  --chip:#E0D8C8;
  --shadow:0 1px 2px rgba(43,38,32,.07), 0 8px 24px -18px rgba(43,38,32,.45);
  --grid-line:#E6DFD2;
}
@media (prefers-color-scheme:dark){
  :root:not([data-theme="light"]):not([data-theme="paper"]){
    --ground:#10161C; --surface:#181F27; --surface-2:#212A34;
    --ink:#E2E8EE; --ink-soft:#A5B2BF; --ink-faint:#7E8B98;
    --rule:#2C3742; --rule-soft:#232C35;
    --comp:#7FB3DA; --comp-wash:#1B2833; --comp-soft:#3E5D75;
    --tens:#E4886C; --tens-wash:#2E2320; 
    --tens-soft:#7A4A38;
    --neut:#8FB8A4; --neut-wash:#1D2724;
    --on-accent:#0D141A;
    --chip:#2A343E;
    --shadow:0 1px 2px rgba(0,0,0,.4), 0 10px 28px -20px rgba(0,0,0,.9);
    --grid-line:#232C35;
  }
}
:root[data-theme="dark"]{
  --ground:#10161C; --surface:#181F27; --surface-2:#212A34;
  --ink:#E2E8EE; --ink-soft:#A5B2BF; --ink-faint:#7E8B98;
  --rule:#2C3742; --rule-soft:#232C35;
  --comp:#7FB3DA; --comp-wash:#1B2833; --comp-soft:#3E5D75;
  --tens:#E4886C; --tens-wash:#2E2320; --tens-soft:#7A4A38;
  --neut:#8FB8A4; --neut-wash:#1D2724;
  --on-accent:#0D141A;
  --chip:#2A343E;
  --shadow:0 1px 2px rgba(0,0,0,.4), 0 10px 28px -20px rgba(0,0,0,.9);
  --grid-line:#232C35;
}

*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{
  margin:0; background:var(--ground); color:var(--ink);
  font-family:"IBM Plex Sans KR","Apple SD Gothic Neo",system-ui,-apple-system,sans-serif;
  line-height:1.7; -webkit-font-smoothing:antialiased;
}
a{color:var(--comp)}
:focus-visible{outline:2px solid var(--comp); outline-offset:2px}

.wrap{max-width:1140px;margin:0 auto;padding:0 22px}
.mono{font-family:"IBM Plex Mono",ui-monospace,monospace}

/* ---------- top bar ---------- */
.topbar{
  border-bottom:1px solid var(--rule); background:var(--surface);
  position:sticky; top:0; z-index:30;
}
.topbar-in{
  max-width:1140px;margin:0 auto;padding:9px 22px;
  display:flex;align-items:center;gap:12px;flex-wrap:wrap;
}
.back{
  display:inline-flex;align-items:center;gap:7px;text-decoration:none;
  font-size:.82rem;color:var(--ink-soft);border:1px solid var(--rule);
  padding:4px 12px;border-radius:999px;background:var(--surface);
  transition:border-color .15s,color .15s;
}
.back:hover{border-color:var(--comp);color:var(--comp)}
.crumb{
  font-family:"IBM Plex Mono",monospace;font-size:.7rem;letter-spacing:.1em;
  text-transform:uppercase;color:var(--ink-faint);
}
.theme-slot{margin-left:auto;display:flex}
.pager{display:flex;gap:6px}
.pager a{
  font-family:"IBM Plex Mono",monospace;font-size:.75rem;text-decoration:none;
  color:var(--ink-soft);border:1px solid var(--rule);border-radius:3px;
  padding:3px 9px;transition:border-color .15s,color .15s;
}
.pager a:hover{border-color:var(--comp);color:var(--comp)}
.pager a[aria-disabled="true"]{opacity:.35;pointer-events:none}


/* --- 배경 테마 전환 --- */
.theme-sw{display:inline-flex;gap:0;border:1px solid var(--rule);border-radius:999px;
  overflow:hidden;background:var(--surface);flex:none}
.theme-sw button{
  font-family:inherit;font-size:.74rem;color:var(--ink-faint);background:transparent;
  border:0;border-right:1px solid var(--rule);padding:4px 10px;cursor:pointer;line-height:1.6;
  transition:background .14s,color .14s;
}
.theme-sw button:last-child{border-right:0}
.theme-sw button:hover{color:var(--comp)}
.theme-sw button[aria-pressed="true"]{background:var(--comp);color:var(--on-accent);font-weight:500}
.theme-sw button:focus-visible{outline:2px solid var(--comp);outline-offset:-2px}
@media (max-width:560px){ .theme-sw button{padding:4px 8px;font-size:.7rem} }

/* ---------- hero ---------- */
.hero{
  padding:34px 0 22px;
  background-image:
    linear-gradient(var(--grid-line) 1px,transparent 1px),
    linear-gradient(90deg,var(--grid-line) 1px,transparent 1px);
  background-size:40px 40px,40px 40px;
  border-bottom:1px solid var(--rule);
}
.hero-in{max-width:1140px;margin:0 auto;padding:0 22px}
.hn{
  display:inline-block;font-family:"IBM Plex Mono",monospace;font-weight:600;
  font-size:.74rem;letter-spacing:.1em;color:var(--on-accent);background:var(--comp);
  padding:2px 9px;border-radius:2px;margin-bottom:12px;
}
h1{
  font-family:"Gowun Batang","Apple SD Gothic Neo",serif;font-weight:700;
  font-size:clamp(1.6rem,4.2vw,2.5rem);line-height:1.25;margin:0 0 12px;
  text-wrap:balance;letter-spacing:-.01em;
}
.lead{max-width:64ch;margin:0;color:var(--ink-soft);font-size:.97rem;font-weight:300}

/* ---------- stage ---------- */
.stage{
  display:grid;grid-template-columns:minmax(0,1.55fr) minmax(280px,1fr);
  gap:16px;margin:24px 0;
}
.viz{
  background:var(--surface);border:1px solid var(--rule);border-radius:4px;
  box-shadow:var(--shadow);padding:12px;position:relative;min-width:0;
}
.viz-scroll{overflow-x:auto;overflow-y:hidden;-webkit-overflow-scrolling:touch}
.viz canvas{display:block;height:auto;touch-action:pan-x pan-y}
.viz-hint{display:none;font-size:.72rem;color:var(--ink-faint);padding:6px 4px 0}
.viz.is-scrollable .viz-hint{display:block}
.viz-cap{
  font-family:"IBM Plex Mono",monospace;font-size:.66rem;letter-spacing:.1em;
  text-transform:uppercase;color:var(--ink-faint);padding:2px 4px 8px;
}
.panel{
  background:var(--surface);border:1px solid var(--rule);border-radius:4px;
  box-shadow:var(--shadow);padding:18px;display:flex;flex-direction:column;gap:16px;
  align-self:start;min-width:0;
}
.panel h2{
  font-family:"IBM Plex Mono",monospace;font-size:.68rem;letter-spacing:.13em;
  text-transform:uppercase;color:var(--ink-faint);margin:0;font-weight:500;
}

/* ---------- controls ---------- */
.ctrl{display:flex;flex-direction:column;gap:5px}
.ctrl-top{display:flex;justify-content:space-between;align-items:baseline;gap:10px}
.ctrl-lab{font-size:.85rem;color:var(--ink-soft)}
.ctrl-val{
  font-family:"IBM Plex Mono",monospace;font-size:.85rem;font-weight:600;
  color:var(--comp);font-variant-numeric:tabular-nums;
}
input[type=range]{
  -webkit-appearance:none;appearance:none;width:100%;height:22px;background:transparent;
  cursor:pointer;margin:0;
}
input[type=range]::-webkit-slider-runnable-track{height:3px;background:var(--rule);border-radius:2px}
input[type=range]::-moz-range-track{height:3px;background:var(--rule);border-radius:2px}
input[type=range]::-webkit-slider-thumb{
  -webkit-appearance:none;width:16px;height:16px;border-radius:50%;
  background:var(--comp);border:2px solid var(--surface);margin-top:-6.5px;
  box-shadow:0 0 0 1px var(--comp);
}
input[type=range]::-moz-range-thumb{
  width:14px;height:14px;border-radius:50%;background:var(--comp);
  border:2px solid var(--surface);box-shadow:0 0 0 1px var(--comp);
}
.seg{display:flex;flex-wrap:wrap;gap:5px}
.seg button{
  font-family:inherit;font-size:.78rem;color:var(--ink-soft);background:var(--surface-2);
  border:1px solid var(--rule);padding:4px 11px;border-radius:3px;cursor:pointer;
  transition:all .14s;
}
.seg button:hover{border-color:var(--comp);color:var(--comp)}
.seg button[aria-pressed="true"]{background:var(--comp);border-color:var(--comp);color:var(--on-accent)}
.tog{
  display:flex;align-items:center;gap:9px;font-size:.85rem;color:var(--ink-soft);
  cursor:pointer;user-select:none;
}
.tog input{
  appearance:none;-webkit-appearance:none;width:34px;height:19px;border-radius:999px;
  background:var(--rule);border:0;position:relative;cursor:pointer;transition:background .15s;flex:none;
}
.tog input::after{
  content:"";position:absolute;top:2.5px;left:2.5px;width:14px;height:14px;border-radius:50%;
  background:var(--surface);transition:transform .15s;
}
.tog input:checked{background:var(--comp)}
.tog input:checked::after{transform:translateX(15px)}
.btn{
  font-family:inherit;font-size:.82rem;padding:7px 14px;border-radius:3px;cursor:pointer;
  background:var(--comp);color:var(--on-accent);border:1px solid var(--comp);transition:opacity .15s;
}
.btn:hover{opacity:.86}
.btn.ghost{background:transparent;color:var(--ink-soft);border-color:var(--rule)}
.btn.ghost:hover{border-color:var(--comp);color:var(--comp);opacity:1}

/* ---------- readouts ---------- */
.reads{display:grid;grid-template-columns:repeat(auto-fit,minmax(112px,1fr));gap:1px;
  background:var(--rule);border:1px solid var(--rule);border-radius:3px;overflow:hidden}
.read{background:var(--surface);padding:9px 11px}
.read .rl{
  display:block;font-family:"IBM Plex Mono",monospace;font-size:.62rem;letter-spacing:.09em;
  text-transform:uppercase;color:var(--ink-faint);margin-bottom:1px;
}
.read .rv{
  font-family:"IBM Plex Mono",monospace;font-size:1.08rem;font-weight:600;
  font-variant-numeric:tabular-nums;line-height:1.3;display:block;
}
.read .ru{font-size:.72rem;color:var(--ink-faint);font-weight:400;margin-left:2px}
.read.is-comp .rv{color:var(--comp)}
.read.is-tens .rv{color:var(--tens)}
.read.is-warn{background:var(--tens-wash)}
.read.is-warn .rv{color:var(--tens)}
.read.is-ok{background:var(--neut-wash)}
.read.is-ok .rv{color:var(--neut)}

/* ---------- callouts / notes ---------- */
.notes{display:grid;grid-template-columns:repeat(auto-fit,minmax(290px,1fr));gap:14px;margin:8px 0 0}
.note{
  background:var(--surface);border:1px solid var(--rule);border-left:3px solid var(--rule);
  border-radius:0 4px 4px 0;padding:15px 18px;font-size:.9rem;color:var(--ink-soft);
}
.note h3{
  margin:0 0 6px;font-family:"IBM Plex Mono",monospace;font-size:.66rem;letter-spacing:.12em;
  text-transform:uppercase;font-weight:600;color:var(--ink-faint);
}
.note.key{border-left-color:var(--comp);background:var(--comp-wash)}
.note.key h3{color:var(--comp)}
.note.mis{border-left-color:var(--tens);background:var(--tens-wash)}
.note.mis h3{color:var(--tens)}
.note p{margin:0}
.note ul{margin:0;padding-left:1.05em}
.note li{margin-bottom:4px}
.note li::marker{color:var(--ink-faint)}
.note strong{color:var(--ink);font-weight:600}
kbd,code{
  font-family:"IBM Plex Mono",monospace;font-size:.88em;background:var(--surface-2);
  padding:.5px 4px;border-radius:2px;color:var(--ink);
}

/* ---------- try list ---------- */
.try{margin:20px 0 0;background:var(--surface);border:1px solid var(--rule);border-radius:4px;padding:18px 20px}
.try h3{
  margin:0 0 10px;font-family:"IBM Plex Mono",monospace;font-size:.66rem;letter-spacing:.12em;
  text-transform:uppercase;color:var(--ink-faint);font-weight:600;
}
.try ol{margin:0;padding-left:1.25em;font-size:.9rem;color:var(--ink-soft)}
.try li{margin-bottom:7px}
.try li::marker{font-family:"IBM Plex Mono",monospace;color:var(--comp);font-weight:600}

/* ---------- formula ---------- */
.eq{
  font-family:"IBM Plex Mono",monospace;background:var(--surface-2);border:1px solid var(--rule);
  border-radius:3px;padding:10px 14px;font-size:.95rem;text-align:center;color:var(--ink);
  overflow-x:auto;white-space:nowrap;
}
.eq small{display:block;font-size:.68rem;color:var(--ink-faint);margin-top:4px;white-space:normal}

footer{
  margin-top:44px;padding:22px 0 46px;border-top:1px solid var(--rule);
  font-family:"IBM Plex Mono",monospace;font-size:.7rem;color:var(--ink-faint);letter-spacing:.04em;
  display:flex;gap:14px;flex-wrap:wrap;align-items:center;
}
footer a{color:var(--ink-faint);text-decoration:none}
footer a:hover{color:var(--comp)}

@media (max-width:880px){
  .stage{grid-template-columns:minmax(0,1fr)}
  .panel{order:2}
}
@media (max-width:560px){
  .wrap,.hero-in,.topbar-in{padding-left:16px;padding-right:16px}
  .hero{padding:24px 0 18px}
  .reads{grid-template-columns:repeat(auto-fit,minmax(96px,1fr))}
}
@media (prefers-reduced-motion:reduce){*{transition:none!important;animation:none!important}}