/*
 * Styled after a pre-war printed chess diagram: paper, ink, boxwood and walnut.
 * Flat colours only; texture comes from an SVG noise tile, never gradients or shadows.
 */
:root {
  --paper: #f1e9d8;
  --ink: #2a2119;
  --ink-soft: #5a4a3a;
  --boxwood: #e6d3a8;
  --walnut: #94704c;
  --rule: #3b2f24;
  --mark: rgba(42, 33, 25, 0.38);
  --last-light: #d9c27f;
  --last-dark: #84693a;
  --check: #a5432d;
  --focus: #1f4e79;
  --serif: 'IM Fell English', 'Iowan Old Style', 'Palatino Linotype', Georgia, serif;
  --serif-sc: 'IM Fell English SC', var(--serif);
  --gutter: 16px;
  --board-size: min(560px, calc(100vw - 2 * var(--gutter) - 2.5rem));
  /* Faint paper grain: a tiled SVG noise filter tinted to sepia. */
  --grain: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='180' height='180'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='.85' numOctaves='2' stitchTiles='stitch'/%3E%3CfeColorMatrix values='0 0 0 0 .3 0 0 0 0 .22 0 0 0 0 .13 0 0 0 .09 0'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)'/%3E%3C/svg%3E");
  /* Engraver's hatching for dark squares, as in printed diagrams. */
  --hatch: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='6' height='6'%3E%3Cpath d='M-1 1l2-2M0 6l6-6M5 7l2-2' stroke='%232a2119' stroke-opacity='.16' stroke-width='.8'/%3E%3C/svg%3E");
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  background-color: var(--paper);
}

body {
  margin: 0;
  padding: 0 var(--gutter) 2rem;
  min-height: 100vh;
  color: var(--ink);
  background-color: var(--paper);
  background-image: var(--grain);
  font-family: var(--serif);
  font-size: 1.0625rem;
  line-height: 1.45;
  overflow-x: hidden;
}

h1,
h2 {
  font-family: var(--serif-sc);
  font-weight: normal;
  letter-spacing: 0.04em;
}

.masthead {
  text-align: center;
  padding: 1.5rem 0 1rem;
  border-bottom: 1px solid var(--rule);
  margin: 0 auto 1.25rem;
  max-width: 1080px;
}

.masthead h1 {
  margin: 0;
  font-size: clamp(1.8rem, 6vw, 2.6rem);
}

.layout {
  display: grid;
  gap: 2rem;
  max-width: 1080px;
  margin: 0 auto;
  justify-content: center;
  grid-template-columns: minmax(0, auto);
}

@media (min-width: 900px) {
  .layout {
    grid-template-columns: auto minmax(280px, 360px);
    align-items: start;
  }
}

.board-area {
  min-width: 0;
}

.caption {
  margin: 0.25rem 0;
  text-align: center;
  font-style: italic;
  color: var(--ink-soft);
  min-height: 1.45em;
}

/* Double rule around the board with coordinates set in the margin. */
.frame {
  display: grid;
  grid-template-columns: 1.25rem var(--board-size);
  grid-template-rows: var(--board-size) 1.25rem;
  justify-content: center;
}

.board {
  grid-column: 2;
  grid-row: 1;
  display: grid;
  grid-template-rows: repeat(8, 1fr);
  width: var(--board-size);
  height: var(--board-size);
  border: 1px solid var(--rule);
  outline: 1px solid var(--rule);
  outline-offset: 3px;
  touch-action: none;
  user-select: none;
}

.board [role='row'] {
  display: grid;
  grid-template-columns: repeat(8, 1fr);
}

.coords {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  font-size: 0.85rem;
  color: var(--ink-soft);
  text-align: center;
}

.coords-ranks {
  grid-column: 1;
  grid-row: 1;
  grid-template-rows: repeat(8, 1fr);
  align-items: center;
  padding-right: 0.45rem;
}

.coords-files {
  grid-column: 2;
  grid-row: 2;
  grid-template-columns: repeat(8, 1fr);
  padding-top: 0.3rem;
}

.square {
  position: relative;
  display: grid;
  place-items: center;
  background-color: var(--boxwood);
}

.square.dark {
  background-color: var(--walnut);
  background-image: var(--hatch);
}

.square.last.light {
  background-color: var(--last-light);
}

.square.last.dark {
  background-color: var(--last-dark);
}

.square.check {
  background-color: var(--check);
}

.square.selected {
  outline: 3px solid var(--ink);
  outline-offset: -3px;
}

.square:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: -3px;
  z-index: 1;
}

.square.target::after {
  content: '';
  position: absolute;
  width: 28%;
  height: 28%;
  border-radius: 50%;
  background-color: var(--mark);
  pointer-events: none;
}

.square.target.occupied::after {
  width: 86%;
  height: 86%;
  background-color: transparent;
  border: 3px solid var(--mark);
}

.piece {
  width: 92%;
  height: 92%;
  pointer-events: none;
  position: relative;
  z-index: 2;
}

.square.dragging-from .piece {
  opacity: 0.35;
}

.drag-ghost {
  position: fixed;
  pointer-events: none;
  z-index: 10;
  transform: translate(-50%, -50%);
}

.status {
  text-align: center;
  font-size: 1.15rem;
  margin: 0.5rem 0 0;
  min-height: 1.6em;
}

.panel {
  display: grid;
  gap: 1.1rem;
  min-width: 0;
}

.panel h2 {
  margin: 0 0 0.4rem;
  font-size: 1.25rem;
  border-bottom: 1px solid var(--rule);
}

.button-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

button,
select,
textarea {
  font: inherit;
  color: var(--ink);
}

button {
  background-color: var(--paper);
  border: 1px solid var(--rule);
  padding: 0.3rem 0.8rem;
  cursor: pointer;
}

button:hover {
  background-color: var(--boxwood);
}

button:focus-visible,
select:focus-visible,
input:focus-visible,
textarea:focus-visible,
summary:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 2px;
}

button:disabled {
  color: var(--ink-soft);
  cursor: default;
  background-color: transparent;
}

.settings {
  border: 1px solid var(--rule);
  margin: 0;
  padding: 0.5rem 0.9rem 0.8rem;
  display: grid;
  gap: 0.55rem;
}

.settings legend {
  font-family: var(--serif-sc);
  padding: 0 0.35rem;
  font-size: 1.1rem;
}

.field {
  display: grid;
  gap: 0.15rem;
}

select {
  background-color: var(--paper);
  border: 1px solid var(--rule);
  padding: 0.2rem;
}

input[type='range'] {
  width: 100%;
  accent-color: var(--walnut);
}

.check {
  display: flex;
  gap: 0.5rem;
  align-items: baseline;
}

input[type='checkbox'] {
  accent-color: var(--walnut);
}

.engine-line {
  margin: 0;
  font-size: 0.9rem;
  font-style: italic;
  color: var(--ink-soft);
  min-height: 1.3em;
  overflow-wrap: anywhere;
}

.move-list {
  list-style: none;
  margin: 0;
  padding: 0;
  max-height: 16rem;
  overflow-y: auto;
  display: grid;
  grid-template-columns: 2.6rem 1fr 1fr;
  align-content: start;
}

.move-list li {
  display: contents;
}

.move-number {
  color: var(--ink-soft);
  padding: 0.1rem 0;
}

.move-list button {
  border: none;
  background-color: transparent;
  text-align: left;
  padding: 0.1rem 0.4rem;
}

.move-list button:hover {
  background-color: var(--boxwood);
}

.move-list button[aria-current='true'] {
  background-color: var(--ink-soft);
  color: var(--paper);
}

textarea {
  width: 100%;
  background-color: var(--paper);
  border: 1px solid var(--rule);
  padding: 0.4rem;
  font-size: 0.9rem;
  resize: vertical;
}

.transfer summary {
  cursor: pointer;
  font-family: var(--serif-sc);
  font-size: 1.1rem;
}

.transfer[open] summary {
  margin-bottom: 0.5rem;
}

.transfer .button-row {
  margin-top: 0.5rem;
}

.error {
  color: var(--check);
  margin: 0.4rem 0 0;
  min-height: 1.2em;
}

.promotion {
  border: 1px solid var(--rule);
  outline: 1px solid var(--rule);
  outline-offset: 3px;
  background-color: var(--paper);
  color: var(--ink);
  padding: 1rem 1.25rem;
}

.promotion::backdrop {
  background-color: rgba(42, 33, 25, 0.35);
}

.promotion h2 {
  margin: 0 0 0.5rem;
  font-size: 1.2rem;
}

.promotion-choices {
  display: flex;
  gap: 0.4rem;
  margin-bottom: 0.75rem;
}

.promotion-choices button {
  width: 3.5rem;
  height: 3.5rem;
  padding: 0.2rem;
  background-color: var(--boxwood);
}

.promotion-choices img {
  width: 100%;
  height: 100%;
}

.colophon {
  max-width: 1080px;
  margin: 2rem auto 0;
  border-top: 1px solid var(--rule);
  text-align: center;
  font-size: 0.9rem;
  color: var(--ink-soft);
}

.colophon a {
  color: var(--ink);
}

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    transition: none !important;
    animation: none !important;
  }
}