:root {
  --brand: #243b6b;
  --accent: #ffb84d;
  --bg: #f4f6fa;
  --panel: #ffffff;
  --panel2: #f8f9fc;
  --text: #1c2333;
  --muted: #667085;
  --line: #dde2ec;
  --input: #ffffff;
  --primary: #2f5bd3;
  --primary-text: #ffffff;
  --danger: #c4372f;
  --shadow: 0 1px 2px rgba(16, 24, 40, .06), 0 2px 8px rgba(16, 24, 40, .05);
  --radius: 10px;
  --mono: ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace;
  --c-alkali: #ffd6d1; --c-alkaline: #ffe6c7; --c-transition: #fdf2c4; --c-post: #d9f2d0;
  --c-metalloid: #cdeee8; --c-nonmetal: #d3e6ff; --c-halogen: #e3dcff; --c-noble: #f5d9f2;
  --c-lanth: #e9f3c9; --c-actin: #ffe0ec;
  /* plot series: fixed categorical order, checked for colour-vision deficiencies */
  --s1: #2a78d6; --s2: #eb6834; --s3: #1baf7a; --s4: #eda100;
  --s5: #e87ba4; --s6: #008300; --s7: #6250d6; --s8: #e34948;
  --grid: #eef1f6;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --brand: #8fb0ff; --accent: #ffb84d; --bg: #0f1420; --panel: #171e2d; --panel2: #1d2537;
    --text: #e6eaf3; --muted: #98a2b8; --line: #2b3550; --input: #111827; --primary: #5b84f0;
    --shadow: 0 1px 2px rgba(0,0,0,.4);
    --c-alkali: #5a2c2a; --c-alkaline: #5a4227; --c-transition: #4f4720; --c-post: #2e4a2a;
    --c-metalloid: #22483f; --c-nonmetal: #243d61; --c-halogen: #3b3263; --c-noble: #4f2c4b;
    --c-lanth: #3d4a22; --c-actin: #57293b;
    --s1: #3987e5; --s2: #d95926; --s3: #199e70; --s4: #c98500;
    --s5: #d55181; --s6: #008300; --s7: #9085e9; --s8: #e66767;
    --grid: #222a3d;
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --brand: #8fb0ff; --accent: #ffb84d; --bg: #0f1420; --panel: #171e2d; --panel2: #1d2537;
  --text: #e6eaf3; --muted: #98a2b8; --line: #2b3550; --input: #111827; --primary: #5b84f0;
  --shadow: 0 1px 2px rgba(0,0,0,.4);
  --c-alkali: #5a2c2a; --c-alkaline: #5a4227; --c-transition: #4f4720; --c-post: #2e4a2a;
  --c-metalloid: #22483f; --c-nonmetal: #243d61; --c-halogen: #3b3263; --c-noble: #4f2c4b;
  --c-lanth: #3d4a22; --c-actin: #57293b;
  --s1: #3987e5; --s2: #d95926; --s3: #199e70; --s4: #c98500;
  --s5: #d55181; --s6: #008300; --s7: #9085e9; --s8: #e66767;
  --grid: #222a3d;
  color-scheme: dark;
}

* { box-sizing: border-box; }
html, body { margin: 0; }
body {
  background: var(--bg); color: var(--text);
  font: 14px/1.45 system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
}
a { color: var(--primary); }
code, pre { font-family: var(--mono); }
.muted { color: var(--muted); }
.hidden { display: none !important; }

/* ------------------------------------------------------------------ top bar */
.topbar {
  position: sticky; top: 0; z-index: 10;
  display: flex; align-items: center; gap: 24px;
  padding: 10px 20px; background: var(--panel); border-bottom: 1px solid var(--line);
}
.brand { display: flex; align-items: center; gap: 10px; min-width: 0; }
.logo { width: 34px; height: 34px; flex: none; }
.brand-name { font-weight: 700; font-size: 17px; letter-spacing: .2px; }
.brand-sub { font-size: 11.5px; color: var(--muted); white-space: nowrap; }
.tabs { display: flex; gap: 4px; flex: 1; overflow-x: auto; scrollbar-width: none; }
.tab {
  border: 0; background: none; color: var(--muted); font: inherit; font-weight: 600;
  padding: 8px 12px; border-radius: 8px; cursor: pointer; white-space: nowrap;
}
.tab:hover { background: var(--panel2); color: var(--text); }
.tab.active { background: var(--brand); color: #fff; }
:root[data-theme="dark"] .tab.active { color: #0f1420; }
@media (prefers-color-scheme: dark) { :root:not([data-theme="light"]) .tab.active { color: #0f1420; } }
.icon-btn {
  display: inline-flex; align-items: center; justify-content: center;
  border: 1px solid var(--line); background: var(--panel); color: var(--text);
  width: 32px; height: 32px; border-radius: 8px; cursor: pointer; font-size: 16px; flex: none; padding: 0;
}

/* ------------------------------------------------------------------ layout */
main { padding: 16px 20px 40px; }
.view { display: none; gap: 16px; align-items: flex-start; }
.view.active { display: flex; }
.panel {
  background: var(--panel); border: 1px solid var(--line); border-radius: var(--radius);
  box-shadow: var(--shadow); padding: 16px;
}
.form-panel { width: 400px; flex: none; position: sticky; top: 72px; max-height: calc(100vh - 88px); overflow: auto; }
.results-panel { flex: 1; min-width: 0; min-height: 560px; }
.prose { width: 100%; max-width: 860px; min-width: 0; margin: 0 auto; overflow-wrap: break-word; }
.prose ul { padding-left: 1.3em; }
.prose code { overflow-wrap: anywhere; }
.prose h2 { margin-top: 0; }
@media (max-width: 960px) {
  .view.active { flex-direction: column; }
  .form-panel { width: 100%; position: static; max-height: none; }
  .results-panel { width: 100%; }
  .brand-sub { display: none; }
  .topbar { gap: 8px 12px; padding: 8px 12px; flex-wrap: wrap; }
  .brand { flex: 1; }
  .tabs { order: 3; flex: 1 1 100%; }
  main { padding: 12px 12px 32px; }
}

h2 { font-size: 13px; text-transform: uppercase; letter-spacing: .6px; color: var(--muted); margin: 18px 0 8px; }
h2:first-child { margin-top: 0; }
.h-note { text-transform: none; letter-spacing: 0; font-weight: 400; }
label { display: block; font-size: 12.5px; color: var(--muted); margin: 6px 0; }
label.inline { display: inline-flex; align-items: center; gap: 6px; margin: 0 12px 0 0; color: var(--text); }
input, select, textarea {
  font: inherit; color: var(--text); background: var(--input);
  border: 1px solid var(--line); border-radius: 7px; padding: 6px 8px; width: 100%;
}
input[type="checkbox"] { width: auto; }
input:focus, select:focus { outline: 2px solid color-mix(in srgb, var(--primary) 40%, transparent); border-color: var(--primary); }
label > input, label > select, label > .unit-input { margin-top: 3px; }
.unit-input { display: flex; }
.unit-input input { border-radius: 7px 0 0 7px; }
.unit-input select { width: auto; border-radius: 0 7px 7px 0; border-left: 0; }
.grid2 { display: grid; grid-template-columns: 1fr 1fr; gap: 8px; align-items: end; }
.grid3 { display: grid; grid-template-columns: 1fr 1fr 1fr; gap: 8px; align-items: end; }
button, .btn {
  font: inherit; font-weight: 600; color: var(--text); background: var(--panel2);
  border: 1px solid var(--line); border-radius: 7px; padding: 6px 12px; cursor: pointer;
  text-decoration: none; display: inline-block;
}
button:hover, .btn:hover { border-color: var(--primary); }
button.primary { background: var(--primary); color: var(--primary-text); border-color: var(--primary); }
button.primary:hover { filter: brightness(1.08); }
button.primary:disabled { opacity: .55; cursor: progress; }
button.danger { color: var(--danger); }
button.wide { width: 100%; margin-top: 14px; padding: 9px; font-size: 14.5px; }
.row-btns { display: flex; gap: 8px; margin-top: 8px; flex-wrap: wrap; }
.hint { font-size: 12px; color: var(--muted); margin: 10px 0 0; }
.small { font-size: 12px; padding: 3px 8px; }

/* ------------------------------------------------------------- ion picker */
.ion-card { display: flex; gap: 12px; align-items: stretch; }
.el-tile {
  width: 64px; height: 64px; border-radius: 9px; border: 1px solid var(--line);
  display: flex; flex-direction: column; align-items: center; justify-content: center;
  cursor: pointer; background: var(--c-nonmetal); flex: none; position: relative;
}
.el-tile:hover { border-color: var(--primary); }
.el-tile .z { position: absolute; top: 3px; left: 6px; font-size: 10px; color: var(--muted); }
.el-tile .sym { font-size: 22px; font-weight: 700; }
.el-tile .nm { font-size: 9.5px; color: var(--muted); max-width: 60px; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.ion-fields { flex: 1; display: grid; grid-template-columns: 1fr 1fr; gap: 6px; }
.ion-fields label { margin: 0; }

/* ----------------------------------------------------------- target editor */
.target-top { display: flex; gap: 8px; }
.target-top select { flex: 1; }
.comp-table { width: 100%; border-collapse: collapse; margin-top: 8px; }
.comp-table th { font-size: 11px; color: var(--muted); font-weight: 600; text-align: left; padding: 2px 4px; }
.comp-table td { padding: 2px 4px; vertical-align: middle; }
.comp-table input { padding: 4px 6px; }
.comp-table .el-chip { cursor: pointer; }
.el-chip {
  display: inline-flex; align-items: center; justify-content: center; min-width: 38px; height: 28px;
  border-radius: 6px; font-weight: 700; border: 1px solid var(--line); background: var(--c-nonmetal);
}
.x-btn { border: 0; background: none; color: var(--muted); cursor: pointer; padding: 2px 6px; font-size: 15px; }
.x-btn:hover { color: var(--danger); }
.adv { display: none; }
.show-adv .adv { display: table-cell; }
.formula-row { display: flex; gap: 6px; margin-top: 8px; }
.formula-row input { font-family: var(--mono); flex: 1; min-width: 0; }
.formula-row button { white-space: nowrap; flex: none; }
.tgt-props { display: grid; grid-template-columns: 1.2fr 1fr .9fr; gap: 8px; align-items: end; margin-top: 6px; }
.tgt-props label { margin: 0; }
.chk { display: flex; align-items: center; gap: 6px; color: var(--text); font-size: 13px; margin: 0 0 6px; }

.layer {
  border: 1px solid var(--line); border-radius: 9px; padding: 10px; margin-bottom: 10px; background: var(--panel2);
}
.layer-head { display: flex; align-items: center; gap: 8px; }
.layer-head .badge { background: var(--brand); color: #fff; border-radius: 6px; padding: 1px 7px; font-size: 12px; font-weight: 700; }
:root[data-theme="dark"] .layer-head .badge { color: #0f1420; }
.layer-head input.lname { flex: 1; font-weight: 600; }
.layer-head .tools { display: flex; gap: 2px; }

/* ---------------------------------------------------------------- results */
.subtabs { display: flex; gap: 4px; border-bottom: 1px solid var(--line); margin: -4px -4px 12px; padding-bottom: 8px; flex-wrap: wrap; }
.subtab { background: none; border: 0; color: var(--muted); padding: 6px 10px; border-radius: 7px; }
.subtab:hover { background: var(--panel2); color: var(--text); }
.subtab.active { color: var(--primary); background: color-mix(in srgb, var(--primary) 12%, transparent); }
.pane { display: none; }
.pane.active { display: block; }
.has-empty .pane, .has-empty .cards { display: none !important; }
.empty { color: var(--muted); padding: 80px 20px; text-align: center; font-size: 15px; }
.plot { width: 100%; height: 470px; }
.plot.tall { height: 640px; }
.toolbar { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; margin-bottom: 8px; }
.table-wrap { overflow: auto; max-height: 620px; border: 1px solid var(--line); border-radius: 8px; }
table.data { border-collapse: collapse; width: 100%; font-variant-numeric: tabular-nums; }
table.data th, table.data td { padding: 5px 10px; text-align: right; border-bottom: 1px solid var(--line); white-space: nowrap; }
table.data th { position: sticky; top: 0; background: var(--panel2); font-size: 12px; color: var(--muted); }
table.data tr:hover td { background: var(--panel2); }
table.mini { width: 100%; border-collapse: collapse; }
table.mini th { font-size: 11px; color: var(--muted); text-align: left; font-weight: 600; padding: 2px 4px; }
table.mini td { padding: 2px 4px; }
pre.srfile {
  font-size: 12px; line-height: 1.35; background: var(--panel2); border: 1px solid var(--line);
  border-radius: 8px; padding: 12px; overflow: auto; max-height: 640px; margin: 0;
}
pre.code { background: var(--panel2); padding: 10px 12px; border-radius: 8px; border: 1px solid var(--line); overflow-x: auto; max-width: 100%; }
.cards { display: grid; grid-template-columns: repeat(auto-fill, minmax(150px, 1fr)); gap: 10px; margin-bottom: 12px; }
.card { border: 1px solid var(--line); border-radius: 9px; padding: 10px 12px; background: var(--panel2); }
.card .k { font-size: 11.5px; color: var(--muted); }
.card .v { font-size: 18px; font-weight: 700; font-variant-numeric: tabular-nums; }
.card .s { font-size: 11.5px; color: var(--muted); }
.canvas-wrap { position: relative; border: 1px solid var(--line); border-radius: 8px; overflow: hidden; background: var(--panel2); }
#tr-canvas { width: 100%; height: 560px; display: block; cursor: crosshair; }
.legend { position: absolute; right: 10px; top: 8px; font-size: 12px; background: color-mix(in srgb, var(--panel) 85%, transparent); border: 1px solid var(--line); border-radius: 7px; padding: 6px 8px; }
.legend span { display: inline-block; width: 12px; height: 3px; margin-right: 6px; vertical-align: middle; }
ul.files { list-style: none; padding: 0; display: flex; flex-wrap: wrap; gap: 6px; }
ul.files a { font-family: var(--mono); font-size: 12.5px; }
ul.curves { list-style: none; padding: 0; margin: 0 0 8px; }
ul.curves li { display: flex; align-items: center; gap: 8px; padding: 4px 0; border-bottom: 1px solid var(--line); font-size: 13px; }
ul.curves li .sw { width: 14px; height: 4px; border-radius: 2px; flex: none; }
ul.curves li .lbl { flex: 1; }

.progress { margin: -4px 0 14px; display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.progress .bar { flex: 1 1 100%; height: 8px; border-radius: 4px; background: var(--panel2); border: 1px solid var(--line); overflow: hidden; }
.progress .fill { height: 100%; width: 0; background: linear-gradient(90deg, var(--primary), var(--accent)); transition: width .3s; }
.progress .ptext { flex: 1; font-size: 12.5px; color: var(--muted); font-variant-numeric: tabular-nums; }

/* ----------------------------------------------------------- periodic table */
dialog#pt-dialog {
  border: 1px solid var(--line); border-radius: 12px; padding: 14px; background: var(--panel); color: var(--text);
  width: min(980px, 96vw); box-shadow: 0 20px 60px rgba(0,0,0,.3);
}
dialog::backdrop { background: rgba(10, 15, 25, .45); }
.pt-head { display: flex; align-items: center; gap: 12px; margin-bottom: 10px; }
.pt-head h3 { margin: 0; font-size: 16px; white-space: nowrap; }
.pt-head input { max-width: 260px; margin-left: auto; }
.pt-grid { display: grid; grid-template-columns: repeat(18, 1fr); gap: 3px; }
.pt-cell {
  aspect-ratio: 1 / 1.05; border-radius: 6px; border: 1px solid var(--line); cursor: pointer;
  display: flex; flex-direction: column; align-items: center; justify-content: center; position: relative;
  font-size: 10px; padding: 0; min-width: 0;
}
.pt-cell .s { font-size: clamp(11px, 1.5vw, 17px); font-weight: 700; }
.pt-cell .z { position: absolute; top: 2px; left: 4px; font-size: 9px; color: var(--muted); }
.pt-cell .m { font-size: 8.5px; color: var(--muted); }
.pt-cell:hover { outline: 2px solid var(--primary); z-index: 1; }
.pt-cell.dim { opacity: .25; }
.pt-cell.na { opacity: .3; cursor: not-allowed; }
.pt-gap { grid-column: span 1; }
.pt-foot { font-size: 12px; margin-top: 8px; }
.cat-alkali { background: var(--c-alkali); } .cat-alkaline { background: var(--c-alkaline); }
.cat-transition { background: var(--c-transition); } .cat-post { background: var(--c-post); }
.cat-metalloid { background: var(--c-metalloid); } .cat-nonmetal { background: var(--c-nonmetal); }
.cat-halogen { background: var(--c-halogen); } .cat-noble { background: var(--c-noble); }
.cat-lanth { background: var(--c-lanth); } .cat-actin { background: var(--c-actin); }

.toast {
  position: fixed; bottom: 20px; left: 50%; transform: translateX(-50%); z-index: 50;
  background: #1f2937; color: #fff; padding: 10px 16px; border-radius: 9px; box-shadow: var(--shadow); max-width: 80vw;
}
.toast.err { background: var(--danger); }
.icon-btn svg { width: 18px; height: 18px; }

.loading { position: fixed; left: 50%; bottom: 24px; transform: translateX(-50%); background: var(--panel, #fff);
  color: var(--text, #222); border: 1px solid var(--line, #ccd); border-radius: 10px; padding: 10px 16px;
  box-shadow: 0 6px 24px rgba(0,0,0,.15); font-size: 14px; z-index: 50; max-width: calc(100% - 32px); }
.loading.hidden { display: none; }

/* ------------------------------------------------------- physics (Markdown) */
/* Physics: chapter list beside the text (desktop), chapter selector above it (narrow) */
.doc-layout { display: grid; grid-template-columns: 250px minmax(0, 860px); justify-content: center; gap: 16px; width: 100%; align-items: start; }
.doc-nav { position: sticky; top: 72px; max-height: calc(100vh - 88px); overflow: auto; padding: 14px 10px 14px 14px; font-size: 13.5px; line-height: 1.4; }
.doc-nav:empty { display: none; }
.doc-nav-title { font-size: 12px; text-transform: uppercase; letter-spacing: .6px; color: var(--muted); font-weight: 600; margin: 0 0 8px 4px; }
.doc-nav ol { list-style: none; margin: 0; padding: 0; }
.doc-nav li.ch > a { display: block; padding: 5px 8px; border-radius: 7px; color: var(--text); text-decoration: none; font-weight: 600; }
.doc-nav li.ch > a:hover { background: var(--panel2); }
.doc-nav li.ch.active > a { background: color-mix(in srgb, var(--primary) 12%, transparent); color: var(--primary); }
.doc-nav li.ch > ol { display: none; margin: 2px 0 6px 10px; padding-left: 8px; border-left: 1px solid var(--line); }
.doc-nav li.ch.active > ol { display: block; }
.doc-nav li.ch > ol a { display: block; padding: 3px 6px; color: var(--muted); text-decoration: none; font-size: 13px; }
.doc-nav li.ch > ol a:hover { color: var(--text); }
.doc-nav .katex { font-size: 1em; }
.doc-select-wrap { display: none; margin: -6px 0 16px; }
.doc-select { width: 100%; font-weight: 600; }
.doc-chapter[hidden] { display: none; }
.doc-chapter > h2:first-child { margin-top: 0; }
.doc-cards { display: grid; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); gap: 10px; margin: 18px 0 6px; }
.doc-card { display: flex; flex-direction: column; gap: 4px; padding: 12px 14px; border: 1px solid var(--line); border-radius: 10px; background: var(--panel2); color: var(--text); text-decoration: none; }
.doc-card:hover { border-color: var(--primary); }
.doc-card .t { font-weight: 650; font-size: 15px; }
.doc-card .s { font-size: 13.5px; line-height: 1.45; color: var(--text); }
.doc-card .n { font-size: 12px; color: var(--muted); line-height: 1.4; }
.doc-pager { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; margin-top: 30px; padding-top: 16px; border-top: 1px solid var(--line); }
.doc-pager a { display: flex; flex-direction: column; padding: 10px 14px; border: 1px solid var(--line); border-radius: 9px; text-decoration: none; color: var(--text); font-weight: 600; font-size: 14px; }
.doc-pager a:hover { border-color: var(--primary); }
.doc-pager small { font-weight: 400; color: var(--muted); font-size: 12px; }
.doc-pager .prev small::before { content: "\2190  "; }
.doc-pager .next { text-align: right; }
.doc-pager .next small::after { content: "  \2192"; }
@media (max-width: 1100px) {
  .doc-layout { grid-template-columns: minmax(0, 860px); }
  .doc-nav { display: none; }
  .doc-select-wrap { display: block; }
}
.doc { position: relative; max-width: 860px; padding: 24px 32px 32px; font-size: 15px; line-height: 1.65; }
.doc > .empty { padding: 60px 0; }
.doc h1, .doc h2, .doc h3, .doc h4 {
  color: var(--text); text-transform: none; letter-spacing: 0; line-height: 1.3;
  scroll-margin-top: 100px; position: relative;
}
.doc h1 { font-size: 26px; margin: 0 0 14px; }
.doc h2 { font-size: 20px; margin: 34px 0 10px; padding-bottom: 6px; border-bottom: 1px solid var(--line); }
.doc h3 { font-size: 16.5px; margin: 26px 0 8px; }
.doc h4 { font-size: 15px; margin: 20px 0 6px; }
.doc h1:first-child { margin-top: 0; }
.doc .anchor {
  margin-left: 8px; color: var(--muted); text-decoration: none; font-weight: 400;
  opacity: 0; transition: opacity .15s;
}
.doc h1:hover .anchor, .doc h2:hover .anchor, .doc h3:hover .anchor, .doc h4:hover .anchor, .doc .anchor:focus { opacity: 1; }
.doc p, .doc ul, .doc ol, .doc blockquote { margin: 0 0 12px; }
.doc ul, .doc ol { padding-left: 1.5em; }
.doc li + li, .doc li > ul, .doc li > ol { margin-top: 3px; }
.doc li > ul, .doc li > ol { margin-bottom: 0; }
.doc blockquote { border-left: 3px solid var(--line); padding: 2px 0 2px 14px; color: var(--muted); }
.doc hr { border: 0; border-top: 1px solid var(--line); margin: 24px 0; }
.doc img { max-width: 100%; height: auto; border-radius: 8px; border: 1px solid var(--line); }
.doc :not(pre) > code {
  font-size: .88em; background: var(--panel2); border: 1px solid var(--line); border-radius: 5px; padding: .05em .35em;
}
.doc pre {
  position: relative;
  font-size: 13px; line-height: 1.5; background: var(--panel2); border: 1px solid var(--line); border-radius: 8px;
  padding: 12px 14px; overflow-x: auto; margin: 0 0 14px;
}
.doc pre code { overflow-wrap: normal; white-space: pre; }
.doc .table-scroll { position: relative; overflow-x: auto; margin: 0 0 14px; border: 1px solid var(--line); border-radius: 8px; }
.doc table { border-collapse: collapse; min-width: 100%; font-size: 14px; line-height: 1.45; }
.doc th, .doc td { padding: 6px 12px; border-bottom: 1px solid var(--line); text-align: left; vertical-align: top; }
.doc th { background: var(--panel2); font-weight: 600; white-space: nowrap; }
.doc tr:last-child td { border-bottom: 0; }
.doc td { font-variant-numeric: tabular-nums; }
/* formulas: KaTeX inherits the text colour; display formulas scroll in their own box */
.doc .katex { font-size: 1.08em; }
.doc .math-display { display: block; position: relative; overflow-x: auto; overflow-y: hidden; margin: 6px 0 14px; padding: 2px 0; }
/* scroll shadows: a shade at the edge where more of the formula is hidden */
.doc .math-display {
  --shade: color-mix(in srgb, var(--text) 22%, transparent);
  background:
    linear-gradient(to right, var(--panel) 40%, transparent) left / 24px 100% no-repeat local,
    linear-gradient(to left, var(--panel) 40%, transparent) right / 24px 100% no-repeat local,
    radial-gradient(farthest-side at 0 50%, var(--shade), transparent) left / 10px 100% no-repeat scroll,
    radial-gradient(farthest-side at 100% 50%, var(--shade), transparent) right / 10px 100% no-repeat scroll;
}
.doc .math-display .katex-display { margin: .4em 0; width: max-content; min-width: 100%; }
/* equation numbers (\tag): room on both sides, so that a wide formula scrolls instead of running under its number */
.doc .math-display .katex-html:has(> .tag) { padding-right: 2.6em; }
.doc .math-display .katex-display > .katex { padding: 0 2px; }

/* ------------------------------------------------------------------ phones */
.tab .ts { display: none; }
.plot { min-height: 0; overflow: hidden; }
.plot.cleared { height: auto; }
.plot + .plot { margin-top: 14px; }
@media (max-width: 640px) {
  body { font-size: 14px; }
  /* 16px inputs: mobile browsers do not zoom in on focus */
  input, select, textarea { font-size: 16px; padding: 7px 8px; }
  .topbar { padding: 6px 12px 0; gap: 4px 8px; }
  .logo { width: 28px; height: 28px; }
  .brand-name { font-size: 16px; }
  .icon-btn { width: 36px; height: 36px; }
  .tabs { margin: 0 -12px; padding: 0 8px 6px; }
  .tab { padding: 8px 10px; font-size: 14px; }
  .tab .tl { display: none; }
  .tab .ts { display: inline; }
  main { padding: 10px 10px 28px; }
  .panel { padding: 12px; border-radius: 9px; }
  .view { gap: 10px; }
  .results-panel { min-height: 0; }
  .empty { padding: 32px 12px; font-size: 14px; }
  .subtabs { flex-wrap: nowrap; overflow-x: auto; scrollbar-width: none; margin: -4px -12px 10px; padding: 0 8px 8px; }
  .subtabs::-webkit-scrollbar, .tabs::-webkit-scrollbar { display: none; }
  .subtab { white-space: nowrap; flex: none; padding: 7px 10px; }
  .plot { height: 400px; }
  .plot.tall { height: 460px; }
  #tr-canvas { height: min(520px, 105vw); }
  .canvas-wrap { overflow: visible; }
  .legend { position: static; display: flex; flex-wrap: wrap; gap: 2px 14px; border: 0; border-top: 1px solid var(--line); border-radius: 0; background: none; padding: 6px 8px; }
  .cards { grid-template-columns: 1fr 1fr; gap: 8px; }
  .card { padding: 8px 10px; }
  .card .v { font-size: 16px; }
  table.data th, table.data td { padding: 4px 8px; font-size: 13px; }
  .table-wrap, pre.srfile { max-height: 70vh; }
  pre.srfile { font-size: 10.5px; }
  .grid3 { grid-template-columns: 1fr 1fr; }
  .ion-card { gap: 10px; }
  /* energy (number + unit) gets a full row; mass and angle share one */
  .ion-fields { grid-auto-flow: row dense; }
  .ion-fields label:has(.unit-input) { grid-column: span 2; }
  .ion-fields .unit-input select { flex: none; width: 5.5em; }
  .el-tile { width: 58px; height: 58px; }
  .tgt-props { grid-template-columns: 1fr 1fr; }
  .tgt-props .chk { grid-column: span 2; }
  .formula-row { flex-wrap: wrap; }
  .formula-row input { flex: 1 1 100%; }
  .formula-row button { flex: 1; }
  .toolbar { gap: 6px 10px; }
  dialog#pt-dialog { width: 100vw; max-width: 100vw; margin: auto 0 0; border-radius: 12px 12px 0 0; padding: 10px; max-height: 88vh; }
  .pt-head { flex-wrap: wrap; gap: 8px; }
  .pt-head input { max-width: none; flex: 1; margin-left: 0; order: 3; flex-basis: 100%; }
  .pt-head .icon-btn { margin-left: auto; }
  .pt-scroll { overflow-x: auto; margin: 0 -10px; padding: 0 10px 4px; }
  .pt-grid { min-width: 600px; }
  .pt-cell .m { display: none; }
  .loading { bottom: 12px; }
  .doc { padding: 16px 14px 20px; font-size: 15px; line-height: 1.6; }
  .doc h1 { font-size: 22px; }
  .doc h2 { font-size: 18px; margin-top: 28px; }
  .doc h3 { font-size: 16px; }
  .doc .anchor { display: none; }
  .doc pre { font-size: 12px; padding: 10px; }
  .doc th, .doc td { padding: 5px 9px; font-size: 13.5px; }
  .doc ul, .doc ol { padding-left: 1.3em; }
}