/* =========================================================================
   BoltLab — visual identity: "indigo drawing on gunmetal", hexagon grid
   (siblings: BeamLab = blue blueprint, FrameLab = teal, ShaftLab = bronze)
   ========================================================================= */
:root {
  --bp-bg: #12131c;
  --bp-bg2: #181926;
  --bp-panel: #1c1d2b;
  --bp-panel2: #252739;
  --bp-line: #323449;
  --bp-line2: #464a66;
  --bp-ink: #e6e6f0;
  --bp-ink-dim: #969ab8;
  --bp-cyan: #9d8cff;          /* primary accent: indigo / violet */
  --bp-blue: #58c6f5;          /* dimensions / secondary */
  --bp-amber: #ffc55c;
  --bp-red: #ff6f8b;
  --bp-green: #5fe3a1;
  --bp-violet: #f0a6ff;
  --bp-pink: #f472b6;
  --bp-steel: #b8bec9;
  --mono: 'Cascadia Code', 'JetBrains Mono', Consolas, 'Courier New', monospace;
  --sans: 'Segoe UI', system-ui, -apple-system, sans-serif;
  --radius: 10px;
}

* { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }

/* Author rules like `.load-grid { display: grid }` outrank the UA stylesheet's
   `[hidden] { display: none }`, so a hidden grid stays visible. Force it. */
[hidden] { display: none !important; }

/* Hexagon lattice — a nut seen head-on, tiled. */
body {
  font-family: var(--sans);
  color: var(--bp-ink);
  background-color: var(--bp-bg);
  background-image:
    url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='56' height='97' viewBox='0 0 56 97'%3E%3Cg fill='none' stroke='%239d8cff' stroke-opacity='0.07' stroke-width='1'%3E%3Cpath d='M28 1 L54 16 L54 46 L28 61 L2 46 L2 16 Z'/%3E%3Cpath d='M28 49.5 L54 64.5 L54 94.5 L28 109.5 L2 94.5 L2 64.5 Z'/%3E%3C/g%3E%3C/svg%3E"),
    linear-gradient(rgba(157, 140, 255, 0.03) 1px, transparent 1px),
    linear-gradient(90deg, rgba(157, 140, 255, 0.03) 1px, transparent 1px);
  background-size: 56px 97px, 168px 168px, 168px 168px;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ------------------------------- Header ------------------------------- */
.app-header {
  position: sticky; top: 0; z-index: 50;
  background: rgba(18, 19, 28, 0.93);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--bp-line);
}
.header-inner {
  max-width: 1480px; margin: 0 auto; padding: 0.7rem 1.2rem;
  display: flex; align-items: center; gap: 1.1rem; flex-wrap: wrap;
}
.back-link {
  color: var(--bp-ink-dim); text-decoration: none; font-size: 1.3rem;
  width: 2.1rem; height: 2.1rem; display: grid; place-items: center;
  border: 1px solid var(--bp-line); border-radius: 8px; transition: 0.2s;
}
.back-link:hover { color: var(--bp-cyan); border-color: var(--bp-cyan); }
.brand { display: flex; align-items: center; gap: 0.6rem; }
.brand-mark { width: 46px; height: 30px; color: var(--bp-cyan); }
.brand-text { display: flex; flex-direction: column; line-height: 1.15; }
.brand-name { font-family: var(--mono); font-weight: 700; font-size: 1.25rem; letter-spacing: 0.04em; }
.brand-name::after { content: '_'; color: var(--bp-blue); animation: blink 1.2s steps(1) infinite; }
@keyframes blink { 50% { opacity: 0; } }
.brand-sub { font-size: 0.72rem; color: var(--bp-ink-dim); letter-spacing: 0.08em; text-transform: uppercase; }

.main-tabs { display: flex; gap: 0.4rem; margin-left: auto; }
.main-tab {
  font-family: var(--mono); font-size: 0.92rem; padding: 0.5rem 1.1rem;
  background: transparent; color: var(--bp-ink-dim);
  border: 1px solid var(--bp-line); border-radius: 8px; cursor: pointer; transition: 0.2s;
}
.main-tab:hover { color: var(--bp-ink); border-color: var(--bp-line2); }
.main-tab.active { color: var(--bp-bg); background: var(--bp-cyan); border-color: var(--bp-cyan); font-weight: 600; }

.lang-toggle { display: flex; border: 1px solid var(--bp-line); border-radius: 8px; overflow: hidden; }
.lang-toggle button {
  font-family: var(--mono); font-size: 0.78rem; padding: 0.42rem 0.6rem;
  background: transparent; color: var(--bp-ink-dim); border: none; cursor: pointer; transition: 0.18s;
}
.lang-toggle button:hover { color: var(--bp-ink); }
.lang-toggle button.active { background: var(--bp-panel2); color: var(--bp-cyan); font-weight: 700; }

/* ------------------------------- Layout ------------------------------- */
main { flex: 1; }
.tab-panel { max-width: 1480px; margin: 0 auto; padding: 1.2rem; }
.calc-layout { display: grid; grid-template-columns: 430px 1fr; gap: 1.2rem; align-items: start; }

.panel {
  background: linear-gradient(180deg, var(--bp-panel), var(--bp-bg2));
  border: 1px solid var(--bp-line);
  border-radius: var(--radius);
  padding: 1rem 1.1rem;
  margin-bottom: 1.2rem;
  position: relative;
}
.panel::before {
  content: ''; position: absolute; inset: 6px; pointer-events: none;
  border: 1px dashed rgba(157, 140, 255, 0.12); border-radius: 6px;
}
.panel-title {
  font-size: 0.95rem; font-weight: 600; letter-spacing: 0.06em; text-transform: uppercase;
  display: flex; align-items: center; gap: 0.55rem; margin-bottom: 0.9rem;
}
.panel-num {
  font-family: var(--mono); font-size: 0.75rem; color: var(--bp-blue);
  border: 1px solid var(--bp-blue); border-radius: 5px; padding: 0.1rem 0.35rem;
}
.panel-title .spacer { margin-left: auto; }

/* ------------------------------- Forms ------------------------------- */
.field-row {
  display: grid; grid-template-columns: 1fr 175px; gap: 0.6rem;
  align-items: center; margin-bottom: 0.55rem;
}
.field-row label { font-size: 0.85rem; color: var(--bp-ink-dim); }
input[type="number"], input[type="text"], select {
  font-family: var(--mono); font-size: 0.88rem;
  background: var(--bp-bg); color: var(--bp-ink);
  border: 1px solid var(--bp-line2); border-radius: 7px;
  padding: 0.4rem 0.5rem; width: 100%;
  transition: border-color 0.2s;
}
input[readonly] { color: var(--bp-cyan); background: rgba(157,140,255,0.07); }
input:focus, select:focus { outline: none; border-color: var(--bp-cyan); }
input[type="number"]::-webkit-inner-spin-button { opacity: 0.4; }
select { cursor: pointer; }
option { background: var(--bp-bg); }

.check-row {
  display: flex; align-items: flex-start; gap: 0.55rem; font-size: 0.83rem;
  color: var(--bp-ink-dim); cursor: pointer; margin-top: 0.55rem; line-height: 1.45;
}
.check-row input { accent-color: var(--bp-cyan); width: 15px; height: 15px; cursor: pointer; margin-top: 2px; flex: none; }

.hint-line { font-size: 0.75rem; color: var(--bp-ink-dim); line-height: 1.55; margin: 0.55rem 0 0.2rem; }
.hint-line strong { color: var(--bp-cyan); font-weight: 600; }

.load-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.45rem; }
.load-grid.three { grid-template-columns: 1fr 1fr 1fr; }
.load-grid.four { grid-template-columns: 1fr 1fr 1fr 1fr; }
.load-grid + .load-grid { margin-top: 0.45rem; }
.mini-field label { display: block; font-size: 0.68rem; color: var(--bp-ink-dim); margin-bottom: 0.15rem; font-family: var(--mono); }
.mini-field input, .mini-field select { padding: 0.3rem 0.42rem; font-size: 0.83rem; }

/* "load an example" — an action bar, deliberately not styled like a setting */
.example-bar {
  display: flex; align-items: center; gap: 0.5rem; flex-wrap: wrap;
  border: 1px dashed var(--bp-line2); border-radius: var(--radius);
  padding: 0.5rem 0.7rem; margin-bottom: 1.2rem;
  background: rgba(157, 140, 255, 0.05);
}
.example-bar > span { font-size: 0.76rem; color: var(--bp-ink-dim); letter-spacing: 0.03em; }
.example-bar select { flex: 1; min-width: 150px; }
.example-bar button {
  font-family: var(--mono); font-size: 0.78rem; padding: 0.4rem 0.8rem; font-weight: 600;
  background: var(--bp-cyan); color: var(--bp-bg); border: none;
  border-radius: 7px; cursor: pointer; transition: 0.2s;
}
.example-bar button:hover { filter: brightness(1.15); }

/* a block of fields belonging to the checkbox above it */
.sub-block {
  border-left: 2px solid var(--bp-line2); margin: 0.15rem 0 0.7rem 0.5rem;
  padding: 0.5rem 0 0.1rem 0.75rem;
}
.sub-block .hint-line { margin-bottom: 0; }

.seg-row { display: flex; gap: 0.3rem; margin-bottom: 0.55rem; flex-wrap: wrap; }
.seg-row.big { flex-direction: column; gap: 0.35rem; margin-bottom: 0.8rem; }
.seg-row.big button {
  display: flex; align-items: center; gap: 0.6rem; text-align: left;
  padding: 0.5rem 0.7rem; font-size: 0.82rem; width: 100%;
}
.seg-row.big button svg { width: 34px; height: 26px; flex: none; color: currentColor; }
.seg-row.big button .jt-sub { display: block; font-size: 0.68rem; opacity: 0.72; }
.seg-row button {
  flex: 1; min-width: 76px; font-family: var(--mono); font-size: 0.76rem;
  padding: 0.36rem 0.4rem; background: transparent; color: var(--bp-ink-dim);
  border: 1px solid var(--bp-line); border-radius: 7px; cursor: pointer; transition: 0.18s;
}
.seg-row button:hover { color: var(--bp-ink); border-color: var(--bp-line2); }
.seg-row button.active { background: var(--bp-panel2); color: var(--bp-cyan); border-color: var(--bp-cyan); font-weight: 600; }

.add-btns { display: flex; gap: 0.4rem; margin-top: 0.4rem; flex-wrap: wrap; }
.btn-add {
  flex: 1; min-width: 78px; display: flex; align-items: center; justify-content: center; gap: 0.35rem;
  font-family: var(--mono); font-size: 0.78rem; padding: 0.45rem 0.3rem;
  background: transparent; color: var(--bp-cyan);
  border: 1px dashed var(--bp-line2); border-radius: 8px; cursor: pointer; transition: 0.2s;
}
.btn-add:hover { border-color: var(--bp-cyan); background: rgba(157, 140, 255, 0.08); }
.btn-add .ico { font-size: 0.95rem; }

/* ------------------------------- Layer / bolt cards ------------------------------- */
.layer-card {
  border: 1px solid var(--bp-line); border-left: 3px solid var(--bp-steel);
  border-radius: 8px; padding: 0.55rem 0.65rem; margin-bottom: 0.5rem;
  background: rgba(18, 19, 28, 0.55);
}
.card-head {
  display: flex; align-items: center; gap: 0.5rem; margin-bottom: 0.45rem;
  font-size: 0.8rem; font-weight: 600; letter-spacing: 0.03em;
}
.card-head .ltag { font-family: var(--mono); color: var(--bp-ink-dim); font-weight: 400; font-size: 0.72rem; }
.icon-btn {
  margin-left: auto; background: none; border: 1px solid var(--bp-line); color: var(--bp-ink-dim);
  border-radius: 6px; min-width: 24px; height: 24px; padding: 0 0.35rem;
  cursor: pointer; line-height: 1; transition: 0.2s; font-size: 0.78rem; font-family: var(--mono);
}
.icon-btn:hover { color: var(--bp-cyan); border-color: var(--bp-cyan); }
.icon-btn.danger:hover { color: var(--bp-red); border-color: var(--bp-red); }
.icon-btn + .icon-btn { margin-left: 0.3rem; }

.info-line { font-family: var(--mono); font-size: 0.73rem; color: var(--bp-ink-dim); margin-top: 0.5rem; line-height: 1.7; }
.info-line b { color: var(--bp-cyan); font-weight: 600; }
.info-line .sep { color: var(--bp-line2); margin: 0 0.35rem; }

/* ------------------------------- Results ------------------------------- */
.schematic-panel svg { width: 100%; height: auto; display: block; }
#jointView { background: rgba(18, 19, 28, 0.5); border: 1px solid var(--bp-line); border-radius: 8px; }
.view-tabs { display: flex; gap: 0.35rem; flex-wrap: wrap; margin-bottom: 0.7rem; }
.view-tabs button {
  font-family: var(--mono); font-size: 0.76rem; padding: 0.3rem 0.7rem;
  background: transparent; color: var(--bp-ink-dim);
  border: 1px solid var(--bp-line); border-radius: 7px; cursor: pointer; transition: 0.18s;
}
.view-tabs button:hover { color: var(--bp-ink); border-color: var(--bp-line2); }
.view-tabs button.active { background: var(--bp-panel2); color: var(--bp-cyan); border-color: var(--bp-cyan); font-weight: 600; }

.solve-error, .solve-warn, .solve-info {
  margin-top: 0.6rem; padding: 0.65rem 0.9rem; border-radius: 8px; font-size: 0.84rem; line-height: 1.55;
}
.solve-error { border: 1px solid var(--bp-red); color: var(--bp-red); background: rgba(255, 111, 139, 0.07); }
.solve-warn { border: 1px solid var(--bp-amber); color: var(--bp-amber); background: rgba(255, 197, 92, 0.07); }
.solve-info { border: 1px solid var(--bp-blue); color: var(--bp-blue); background: rgba(88, 198, 245, 0.07); }
.solve-warn ul, .solve-info ul, .solve-error ul { margin: 0.3rem 0 0 1.1rem; }

.result-cards {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 0.8rem; margin-bottom: 1.2rem;
}
.rcard {
  background: linear-gradient(180deg, var(--bp-panel), var(--bp-bg2));
  border: 1px solid var(--bp-line); border-radius: var(--radius); padding: 0.75rem 0.9rem;
}
.rcard .rc-label {
  font-size: 0.67rem; text-transform: uppercase; letter-spacing: 0.09em;
  color: var(--bp-ink-dim); margin-bottom: 0.3rem; display: flex; justify-content: space-between; gap: 0.4rem;
}
.rcard .rc-value { font-family: var(--mono); font-size: 1.22rem; font-weight: 700; }
.rcard .rc-value small { font-size: 0.72rem; color: var(--bp-ink-dim); font-weight: 400; }
.rcard .rc-sub { font-family: var(--mono); font-size: 0.7rem; color: var(--bp-ink-dim); margin-top: 0.25rem; line-height: 1.55; }
.rcard.ok { border-left: 3px solid var(--bp-green); }
.rcard.bad { border-left: 3px solid var(--bp-red); }
.rcard.warn { border-left: 3px solid var(--bp-amber); }
.rcard.neutral { border-left: 3px solid var(--bp-cyan); }

.util-bar { height: 7px; background: var(--bp-bg); border-radius: 4px; margin-top: 0.45rem; overflow: hidden; border: 1px solid var(--bp-line); }
.util-fill { height: 100%; border-radius: 3px; background: var(--bp-green); transition: width 0.3s; }
.util-fill.bad { background: var(--bp-red); }
.util-fill.warn { background: var(--bp-amber); }

.chart-panel { padding-bottom: 0.6rem; }
.chart-head { display: flex; align-items: baseline; justify-content: space-between; margin-bottom: 0.4rem; gap: 0.6rem; }
.chart-head h3 { font-size: 0.88rem; font-weight: 600; letter-spacing: 0.04em; }
.chart-max { font-family: var(--mono); font-size: 0.77rem; color: var(--bp-blue); white-space: nowrap; }
.chart-panel svg { width: 100%; display: block; }
.chart-note { font-size: 0.72rem; color: var(--bp-ink-dim); margin-top: 0.4rem; font-style: italic; line-height: 1.55; }

.res-table { border-collapse: collapse; width: 100%; font-size: 0.78rem; font-family: var(--mono); }
.res-table th, .res-table td { border: 1px solid var(--bp-line); padding: 0.4rem 0.55rem; text-align: left; white-space: nowrap; }
.res-table th { background: var(--bp-panel2); color: var(--bp-cyan); font-weight: 600; }
.res-table td.ok, .res-table td .ok { color: var(--bp-green); }
.res-table td.bad, .res-table td .bad { color: var(--bp-red); }
.res-table td.warn, .res-table td .warn { color: var(--bp-amber); }
.res-table td.dim { color: var(--bp-ink-dim); white-space: normal; }
.res-table tr.rowbad td:first-child { border-left: 3px solid var(--bp-red); }
.res-table tr.rowok td:first-child { border-left: 3px solid var(--bp-green); }
.res-table tr.rowwarn td:first-child { border-left: 3px solid var(--bp-amber); }
.tbl-wrap { overflow-x: auto; }

/* ------------------------------- Textbook ------------------------------- */
.learn-layout { display: grid; grid-template-columns: 300px 1fr; gap: 1.2rem; align-items: start; }
.learn-nav {
  position: sticky; top: 76px;
  background: linear-gradient(180deg, var(--bp-panel), var(--bp-bg2));
  border: 1px solid var(--bp-line); border-radius: var(--radius); padding: 0.7rem; overflow: hidden;
}
.learn-nav button {
  display: flex; align-items: center; gap: 0.6rem; width: 100%; text-align: left;
  background: none; border: none; color: var(--bp-ink-dim); cursor: pointer;
  padding: 0.55rem 0.7rem; border-radius: 8px; font-size: 0.87rem; transition: 0.15s; font-family: var(--sans);
}
.learn-nav button:hover { background: rgba(157, 140, 255, 0.08); color: var(--bp-ink); }
.learn-nav button.active { background: rgba(157, 140, 255, 0.14); color: var(--bp-cyan); font-weight: 600; }
.learn-nav .ch-num { font-family: var(--mono); font-size: 0.7rem; color: var(--bp-blue); min-width: 1.5rem; }

.learn-body {
  background: linear-gradient(180deg, var(--bp-panel), var(--bp-bg2));
  border: 1px solid var(--bp-line); border-radius: var(--radius); padding: 1.6rem 2rem;
  line-height: 1.75; font-size: 0.97rem;
}
.learn-body h2 { font-size: 1.45rem; margin-bottom: 1rem; }
.learn-body h3 { font-size: 1.08rem; margin: 1.6rem 0 0.6rem; color: var(--bp-cyan); }
.learn-body h4 { font-size: 0.97rem; margin: 1.1rem 0 0.4rem; color: var(--bp-blue); }
.learn-body p { margin-bottom: 0.8rem; }
.learn-body ul, .learn-body ol { margin: 0 0 0.9rem 1.4rem; }
.learn-body li { margin-bottom: 0.35rem; }
.learn-body strong { color: var(--bp-amber); font-weight: 600; }
.learn-body em { color: var(--bp-ink-dim); }
.learn-body code { font-family: var(--mono); font-size: 0.88em; color: var(--bp-blue); background: var(--bp-bg); padding: 0.05rem 0.3rem; border-radius: 4px; }
.learn-body table { border-collapse: collapse; width: 100%; margin: 0.8rem 0 1.1rem; font-size: 0.85rem; }
.learn-body th, .learn-body td { border: 1px solid var(--bp-line2); padding: 0.45rem 0.6rem; text-align: left; }
.learn-body th { background: var(--bp-panel2); font-weight: 600; color: var(--bp-cyan); }
.learn-body .tbl-wrap { margin: 0.8rem 0 1.1rem; }
.learn-body .tbl-wrap table { margin: 0; }

.formula {
  font-family: var(--mono); text-align: center; margin: 1rem auto; padding: 0.8rem 1rem;
  background: var(--bp-bg); border: 1px solid var(--bp-line2); border-radius: 8px;
  font-size: 1.02rem; overflow-x: auto;
  display: flex; align-items: center; justify-content: center; gap: 0.4rem; flex-wrap: wrap;
}
.formula .tag { font-family: var(--sans); font-size: 0.7rem; color: var(--bp-ink-dim); align-self: flex-end; }
.fx { font-family: var(--mono); color: var(--bp-cyan); white-space: nowrap; }
.frac { display: inline-flex; flex-direction: column; vertical-align: middle; text-align: center; margin: 0 0.25rem; }
.frac > span { display: block; padding: 0 0.35rem; }
.frac > span:first-child { border-bottom: 1.5px solid currentColor; }
sub, sup { font-size: 0.68em; }

.note-box {
  border-left: 3px solid var(--bp-blue); background: rgba(88, 198, 245, 0.06);
  border-radius: 0 8px 8px 0; padding: 0.7rem 1rem; margin: 0.9rem 0; font-size: 0.9rem;
}
.warn-box {
  border-left: 3px solid var(--bp-red); background: rgba(255, 111, 139, 0.06);
  border-radius: 0 8px 8px 0; padding: 0.7rem 1rem; margin: 0.9rem 0; font-size: 0.9rem;
}
.src-box {
  border-left: 3px solid var(--bp-violet); background: rgba(240, 166, 255, 0.05);
  border-radius: 0 8px 8px 0; padding: 0.7rem 1rem; margin: 0.9rem 0; font-size: 0.84rem;
}
.src-box b { color: var(--bp-violet); }
.example-box { border: 1px solid var(--bp-green); border-radius: 8px; padding: 1rem 1.2rem; margin: 1rem 0; }
.example-box .ex-title { font-weight: 700; color: var(--bp-green); margin-bottom: 0.5rem; font-size: 0.92rem; letter-spacing: 0.04em; text-transform: uppercase; }
.try-btn {
  display: inline-block; margin-top: 0.5rem; font-family: var(--mono); font-size: 0.82rem;
  color: var(--bp-bg); background: var(--bp-cyan); border: none; border-radius: 7px;
  padding: 0.45rem 0.9rem; cursor: pointer; transition: 0.2s; font-weight: 600;
}
.try-btn:hover { filter: brightness(1.15); }

.learn-fig { margin: 1.2rem auto; text-align: center; }
.learn-fig svg { max-width: 100%; height: auto; }
.learn-fig figcaption { font-size: 0.78rem; color: var(--bp-ink-dim); margin-top: 0.4rem; font-style: italic; }

/* ------------------------------- Footer ------------------------------- */
.app-footer {
  border-top: 1px solid var(--bp-line); padding: 1rem 1.2rem; text-align: center;
  font-size: 0.8rem; color: var(--bp-ink-dim);
}
.app-footer a { color: var(--bp-cyan); text-decoration: none; }
.app-footer a:hover { text-decoration: underline; }

/* ------------------------------- Responsive ------------------------------- */
@media (max-width: 1200px) {
  .calc-layout { grid-template-columns: 1fr; }
  .learn-layout { grid-template-columns: 1fr; }
  .learn-nav { position: static; display: flex; flex-wrap: wrap; gap: 0.3rem; }
  .learn-nav button { width: auto; }
}
@media (max-width: 640px) {
  .header-inner { gap: 0.6rem; }
  .brand-sub { display: none; }
  .main-tabs { order: 3; width: 100%; margin-left: 0; }
  .main-tab { flex: 1; }
  .learn-body { padding: 1.1rem 1rem; }
  .load-grid.three, .load-grid.four { grid-template-columns: 1fr 1fr; }
  .field-row { grid-template-columns: 1fr; }
}