:root,
:root[data-theme="dark"] {
  --bg: #0b0d11;
  --panel: #12151c;
  --panel-2: #171b24;
  --line: #242a36;
  --text: #e6e9f0;
  --dim: #8b93a7;
  --accent: #f5b942;
  --accent-2: #6fa8ff;
  --shadow: 0 18px 50px rgba(0, 0, 0, 0.55);
}

:root[data-theme="light"] {
  --bg: #f2f4f7;
  --panel: #ffffff;
  --panel-2: #f0f2f6;
  --line: #d9dee7;
  --text: #14181f;
  --dim: #5d6678;
  --accent: #c8860a;
  --accent-2: #2563c9;
  --shadow: 0 18px 50px rgba(20, 30, 60, 0.18);
}

:root {
  --radius: 9px;
  --mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
}

* { box-sizing: border-box; }

html, body { height: 100%; margin: 0; }

body {
  background: var(--bg);
  color: var(--text);
  font: 13.5px/1.5 ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

kbd {
  font: 11px var(--mono);
  padding: 0.5px 4px;
  border: 1px solid var(--line);
  border-bottom-width: 2px;
  border-radius: 4px;
  background: var(--panel-2);
  color: var(--text);
}

/* ------------------------------------------------------------------ header */

header {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 7px 12px;
  border-bottom: 1px solid var(--line);
  background: var(--panel);
  flex: none;
}
header h1 {
  margin: 0;
  font-size: 15px;
  font-weight: 650;
  letter-spacing: -0.01em;
  white-space: nowrap;
}
header h1::before { content: "✦"; color: var(--accent); margin-right: 6px; }
header a.ghost { text-decoration: none; display: inline-block; }
.spacer { flex: 1; }
.dim { color: var(--dim); }

#stats { font-size: 12px; white-space: nowrap; }
#stats b { color: var(--text); font-weight: 600; }

.picker {
  display: flex;
  align-items: center;
  gap: 7px;
  padding: 3px 9px 3px 3px;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--panel-2);
  color: var(--text);
  font: inherit;
  font-size: 13px;
  cursor: pointer;
  white-space: nowrap;
}
.picker img { width: 24px; height: 24px; border-radius: 50%; background: #fff; object-fit: contain; }
.picker b { color: var(--dim); font-weight: 400; }
.picker:hover { border-color: var(--accent); }

/* ------------------------------------------------------------------ layout */

main {
  flex: 1;
  min-height: 0;
  display: grid;
  grid-template-columns: minmax(0, 1fr) 322px;
  gap: 1px;
  background: var(--line);
}

.stage {
  background: var(--panel);
  display: flex;
  flex-direction: column;
  min-width: 0;
  min-height: 0;
}

.views {
  flex: 1;
  min-height: 0;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1px;
  background: var(--line);
}

.view { position: relative; min-width: 0; min-height: 0; background: var(--bg); }
.view canvas {
  position: absolute; inset: 0;
  width: 100%; height: 100%;
  display: block;
  touch-action: none;
}
.view-label {
  position: absolute; left: 0; right: 0; bottom: 0;
  display: flex; gap: 10px;
  padding: 6px 10px;
  font-size: 11px;
  color: var(--dim);
  background: linear-gradient(transparent, color-mix(in srgb, var(--bg) 90%, transparent));
  pointer-events: none;
}
.hover { margin-left: auto; color: var(--accent); font-family: var(--mono); }
.nogl { display: grid; place-items: center; height: 100%; padding: 20px; color: var(--dim); text-align: center; }

.statusbar {
  flex: none;
  position: relative;
  padding: 6px 12px;
  border-top: 1px solid var(--line);
  font: 11.5px var(--mono);
  color: var(--dim);
}
#status.busy { color: var(--accent); }
#progress {
  position: absolute; top: -1px; left: 0;
  height: 2px;
  width: calc(var(--frac, 0) * 100%);
  background: var(--accent);
  transition: width 0.12s linear;
}

/* ------------------------------------------------------------------ right panel */

.panel.right {
  background: var(--panel);
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  min-height: 0;
}

.group { padding: 9px 11px; border-bottom: 1px solid var(--line); }

h2 {
  margin: 0;
  font-size: 11px;
  font-weight: 650;
  letter-spacing: 0.07em;
  text-transform: uppercase;
  color: var(--dim);
}

details.group > summary {
  list-style: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 6px;
  user-select: none;
}
details.group > summary::-webkit-details-marker { display: none; }
details.group > summary::before { content: "▸"; font-size: 9px; color: var(--dim); }
details.group[open] > summary::before { content: "▾"; }
details.group > summary:hover h2 { color: var(--text); }
details.group[open] > summary { margin-bottom: 7px; }

/* ---- cells table ---- */

.cells-group { display: flex; flex-direction: column; }
.group-head { display: flex; flex-direction: column; gap: 6px; margin-bottom: 7px; }

.cells-wrap {
  flex: none;
  height: 200px;
  min-height: 90px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  overflow: hidden;
  background: var(--panel);
}
#cells { display: block; width: 100%; height: 100%; }

.info {
  min-height: 16px;
  margin-top: 5px;
  font-size: 10.5px;
  color: var(--accent);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

/* ---- controls ---- */

.row { display: flex; gap: 5px; flex-wrap: wrap; }
.row + .row { margin-top: 5px; }
.buttons button, .filebtn, .ghost {
  flex: 1 1 auto;
  padding: 4px 8px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--panel-2);
  color: var(--text);
  font: inherit;
  font-size: 12px;
  cursor: pointer;
  white-space: nowrap;
}
.buttons.tight button { padding: 3px 6px; font-size: 11.5px; }
.buttons button:hover, .filebtn:hover, .ghost:hover { border-color: var(--accent); color: var(--accent); }
.ghost { flex: none; }
.ghost.icon { width: 30px; text-align: center; padding: 4px 0; }

.filebtn { display: block; margin-top: 5px; text-align: center; }
.filebtn.inline { margin-top: 0; }
.filebtn input { display: none; }
.buttons button.primary {
  background: color-mix(in srgb, var(--accent) 18%, var(--panel-2));
  border-color: color-mix(in srgb, var(--accent) 45%, var(--line));
  font-weight: 600;
}
.note code {
  font: 11px var(--mono);
  padding: 0 3px;
  border-radius: 3px;
  background: var(--panel-2);
}

.field {
  display: flex; align-items: center; gap: 8px;
  margin: 5px 0;
  font-size: 12px;
  color: var(--dim);
}
.field > span { flex: none; min-width: 84px; }
.field > span b { color: var(--accent); font-family: var(--mono); }
.field select, .field input[type="number"] {
  flex: 1; min-width: 0;
  padding: 3px 6px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--panel-2);
  color: var(--text);
  font: inherit; font-size: 12px;
}
.field input[type="range"] { flex: 1; accent-color: var(--accent); }

.check {
  display: flex; align-items: center; gap: 6px;
  padding: 2px 0;
  font-size: 12.5px;
  cursor: pointer;
}
.check input { accent-color: var(--accent); }

.note { margin: 6px 0 2px; font-size: 11px; line-height: 1.5; color: var(--dim); }

#cellsString {
  width: 100%;
  margin-top: 6px;
  padding: 4px 7px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--panel-2);
  color: var(--accent);
  font-family: var(--mono);
  font-size: 11px;
}

/* ------------------------------------------------------------------ dialogs */

dialog {
  border: 1px solid var(--line);
  border-radius: 14px;
  background: var(--panel);
  color: var(--text);
  box-shadow: var(--shadow);
  padding: 0;
}
dialog::backdrop { background: rgba(0, 0, 0, 0.55); backdrop-filter: blur(2px); }

/* Only style the open state with `display`: a bare `display: flex` here would
   beat the UA's `dialog:not([open]) { display: none }` and leave it always up. */
#catalogDialog {
  width: min(860px, 94vw);
  height: min(600px, 88vh);
  overflow: hidden;
}
#catalogDialog[open] { display: flex; flex-direction: column; }

.cat-head {
  display: flex; gap: 8px; align-items: center;
  padding: 12px 14px 10px;
  flex: none;
}
#search {
  flex: 1;
  padding: 7px 11px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--panel-2);
  color: var(--text);
  font: inherit; font-size: 13px;
}
#search::placeholder { color: var(--dim); }
#search:focus { outline: 2px solid var(--accent-2); outline-offset: -1px; }

.cat-chips {
  display: flex; gap: 5px;
  padding: 0 14px 10px;
  overflow-x: auto;
  scrollbar-width: none;
  border-bottom: 1px solid var(--line);
  flex: none;
}
.cat-chips::-webkit-scrollbar { display: none; }
.chip {
  flex: none;
  padding: 3px 10px;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: none;
  color: var(--dim);
  font: inherit; font-size: 11.5px;
  white-space: nowrap;
  cursor: pointer;
}
.chip:hover { border-color: var(--accent); color: var(--accent); }

#catalog { flex: 1; overflow-y: auto; padding: 0 14px 14px; }
.scroll { overscroll-behavior: contain; }

.cat h3 {
  position: sticky; top: 0; z-index: 1;
  display: flex; align-items: center; gap: 8px;
  margin: 0;
  padding: 12px 2px 6px;
  font-size: 10.5px; font-weight: 650;
  letter-spacing: 0.08em; text-transform: uppercase;
  color: var(--dim);
  background: linear-gradient(var(--panel) 72%, transparent);
}
.cat h3 em { font-style: normal; opacity: 0.6; font-size: 10px; }
.cat h3::after {
  content: ""; flex: 1; height: 1px;
  background: var(--line);
}

/* the specimen grid: thumbnails only, names live in the footer */
.grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(50px, 1fr));
  gap: 4px;
}

.poly {
  aspect-ratio: 1;
  padding: 0;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: #fff;
  overflow: hidden;
  cursor: pointer;
  transition: transform 0.09s ease, border-color 0.09s ease, box-shadow 0.09s ease;
}
.poly img {
  width: 100%; height: 100%;
  display: block;
  object-fit: contain;
}
:root[data-theme="dark"] .poly { filter: brightness(0.9); }
.poly:hover, .poly:focus-visible {
  border-color: var(--accent);
  transform: translateY(-1px) scale(1.06);
  box-shadow: 0 4px 14px rgba(0, 0, 0, 0.28);
  outline: none;
  filter: none;
  z-index: 2;
  position: relative;
}
.poly.active {
  border-color: var(--accent);
  box-shadow: 0 0 0 2px var(--accent);
  filter: none;
}

.cat-foot {
  display: flex; align-items: center; gap: 10px;
  padding: 9px 14px;
  border-top: 1px solid var(--line);
  background: var(--panel-2);
  flex: none;
  min-height: 54px;
}
.cat-foot img {
  width: 34px; height: 34px;
  border-radius: 6px;
  background: #fff;
  object-fit: contain;
  flex: none;
}
.cat-foot-text { display: flex; flex-direction: column; min-width: 0; line-height: 1.35; }
#footName { font-size: 13.5px; font-weight: 600; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
#footMeta { font-size: 11px; font-family: var(--mono); white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
#footCount { margin-left: auto; font-size: 11px; white-space: nowrap; }

#helpDialog { max-width: 620px; padding: 22px 26px 20px; line-height: 1.62; }
#helpDialog h2 { font-size: 18px; text-transform: none; letter-spacing: -0.01em; color: var(--text); margin-bottom: 10px; }
#helpDialog h3 { margin: 18px 0 6px; font-size: 12px; letter-spacing: 0.05em; text-transform: uppercase; color: var(--dim); }
#helpDialog ul { padding-left: 18px; margin: 6px 0; }
#helpDialog li { margin: 6px 0; }
#helpDialog a { color: var(--accent-2); }
#helpClose {
  margin-top: 18px; padding: 6px 16px;
  border: 1px solid var(--line); border-radius: var(--radius);
  background: var(--panel-2); color: var(--text);
  font: inherit; cursor: pointer;
}
#helpClose:hover { border-color: var(--accent); color: var(--accent); }

/* ------------------------------------------------------------------ narrow */

@media (max-width: 1080px) {
  main { grid-template-columns: minmax(0, 1fr) 290px; }
  .views { grid-template-columns: 1fr; grid-template-rows: 1fr 1fr; }
}

@media (max-width: 780px) {
  body { overflow: auto; }
  main { grid-template-columns: 1fr; grid-auto-rows: min-content; }
  .stage { min-height: 520px; }
  .views { grid-template-rows: 260px 260px; }
  .panel.right { max-height: none; }
  #stats { display: none; }
}

/* the key to the Cells bar colours */
.legend {
  display: flex;
  align-items: center;
  gap: 7px;
  flex-wrap: wrap;
  margin-top: 7px;
  font-size: 10.5px;
  color: var(--dim);
}
.legend-label { letter-spacing: 0.04em; text-transform: uppercase; font-size: 9.5px; }
.legend-item { display: inline-flex; align-items: center; gap: 3px; font-family: var(--mono); }
.legend-item i { width: 11px; height: 3px; border-radius: 2px; display: inline-block; }
.note a { color: var(--accent-2); text-decoration: none; }
.note a:hover { text-decoration: underline; }

/* the Cells shortcut key — one line per gesture, compact */
.note.keys { list-style: none; margin: 5px 0 3px; padding: 0; }
.note.keys li {
  display: flex;
  align-items: baseline;
  gap: 6px;
  padding: 1.5px 0;
  white-space: nowrap;
}
.note.keys kbd { flex: none; }

/* ------------------------------------------------ draggable pane splitters */

main { grid-template-columns: minmax(0, 1fr) 6px var(--panel-w, 322px); }
.views { grid-template-columns: var(--views-a, 1fr) 6px var(--views-b, 1fr); }

.splitter {
  background: var(--line);
  cursor: col-resize;
  position: relative;
  transition: background 0.12s ease;
}
.splitter::after {                 /* a fatter invisible grab area */
  content: "";
  position: absolute;
  inset: 0 -4px;
}
.splitter:hover, .splitter.dragging { background: var(--accent); }

@media (max-width: 900px) {
  main { grid-template-columns: minmax(0, 1fr); }
  .splitter.vertical { display: none; }
}

/* ------------------------------------------------ always-visible view tools */

.view { position: relative; }
.view-tools {
  position: absolute;
  top: 8px;
  left: 8px;
  display: flex;
  gap: 5px;
  z-index: 5;
}
.view-tools button {
  padding: 3px 10px;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: color-mix(in srgb, var(--panel) 88%, transparent);
  color: var(--dim);
  font: inherit;
  font-size: 11.5px;
  cursor: pointer;
  backdrop-filter: blur(4px);
}
.view-tools button:hover { border-color: var(--accent); color: var(--accent); }

/* -------------------------------------------------- add / remove, one palette

   Green adds, red carves, and the pair reads the same in the 3-D view, in the
   diagram and in the Cells table. Keeping the words in the captions the same
   colour as the outline that appears under the pointer is what ties the three
   together — before, each view had its own idea of what a highlight looked like.
   Kept identical in light and dark: these are signal colours, not decoration. */
:root { --add: #2fa855; --rem: #d63c3c; }
:root[data-theme="dark"] { --add: #4acb70; --rem: #f05454; }
.add { color: var(--add); }
.rem { color: var(--rem); }

/* the three symmetry-element toggles, boxed so they read as one control */
.sym-elems {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 4px 8px 6px;
  margin: 6px 0 4px;
}
.sym-elems legend { font-size: 10.5px; color: var(--dim); padding: 0 4px; }
.sym-elems .check { margin: 2px 0; }
.sw {
  display: inline-block; width: 9px; height: 9px; border-radius: 2px;
  vertical-align: baseline; margin-right: 1px;
}
.sw.ax { background: #40b8f2; }
.sw.mi { background: #6be0cc; }
.sw.im { background: #b873f2; }

/* undo / redo sit with the other cell buttons and grey out when there is
   nothing to undo — the disabled state is the only affordance saying whether a
   change has been made yet */
.buttons button.icon { width: 26px; padding: 4px 0; text-align: center; }
.buttons button:disabled { opacity: 0.35; cursor: default; }
.buttons button:disabled:hover { border-color: var(--line); color: inherit; }

/* the diagram's two toggle colours — gold beneath the plane, blue above */
:root { --below: #b98d10; --above: #2f7cc9; }
:root[data-theme="dark"] { --below: #f5d24d; --above: #4da3f5; }
.below { color: var(--below); }
.above { color: var(--above); }

/* element checkboxes grey out when the group has none of that kind */
.sym-elems .check.off { opacity: 0.4; }
.elem-legend { margin-top: 4px; }
.elem-legend:empty { display: none; }

/* the make-planes sheet */
#planesDialog { width: min(560px, 92vw); }
#planesDialog textarea {
  width: 100%; box-sizing: border-box; resize: vertical;
  background: var(--panel); color: var(--text);
  border: 1px solid var(--line); border-radius: 8px; padding: 8px;
  font-size: 12px; line-height: 1.5;
}

/* Narrow screens: the header is a flex row and its children overrun a phone,
   pushing the theme toggle and the help button off-screen where they cannot be
   reached. Wrapping the row instead would make it taller and break the
   scroll-margin the section anchors depend on, so secondary links marked
   `optional` are hidden below 650px. Same rule already used on historical.html. */
@media (max-width: 650px) {
  .doc-head .optional, header .optional { display: none; }
}