:root {
    --border-width: calc(var(--diameter-tile) / 60);
    --diameter-board: min(85vw, 85vh);
    --diameter-tile: calc(1 / 8 * var(--diameter-board));
    --edge-width: calc((min(100vw, 100vh) - var(--diameter-board)) * 0.3);
    --color-danger: tomato;
    --color-success: #1d83e0;
    --color-white: #f0f0f0;
    --color-black: #222;
    --color-board-hue: 30;
    --color-board-sat: 40%;
    --color-shadow: hsl(var(--color-board-hue), var(--color-board-sat), 50%);
    --color-shadow-lighter: hsl(var(--color-board-hue), var(--color-board-sat), 55%);
    --transition-ease: cubic-bezier(0.25, 1, 0.5, 1);
    --color-background: var(--color-black);
}

aside {
    display: flex;
    justify-content: space-between;
    left: 0;
    position: absolute;
    top: calc(var(--edge-width) * -0.55);
    transform: translateY(-50%);
    width: 100%;
    z-index: 999;
}

aside div {
    align-items: center;
    color: white;
    display: flex;
}

aside div > * {
    align-items: center;
    display: flex;
}

aside div > * + * {
    margin-left: calc(var(--border-width) * 2);
}

aside div h3,
aside div label {
    font-size: calc(var(--edge-width) * 0.3);
    height: calc(var(--edge-width) * 0.3);
    line-height: 1;
    margin-bottom: 0;
    margin-top: 0;
    text-transform: uppercase;
}

aside div label {
    cursor: pointer;
}

aside div input {
    left: -99999px;
    position: absolute;
}

aside div input + * {
    opacity: 0.5;
}

aside div input:checked + * {
    font-weight: bold;
    opacity: 1;
}

aside div svg {
    height: calc(var(--edge-width) * 0.5);
    width: auto;
}

html,
body {
    height: 100%;
}

body {
    background: var(--color-background);
    overflow: hidden;
    transition: background-color 250ms ease-in-out;

    display: flex;
    align-items: center;
    justify-content: center;
}

#view {
    background: var(--color-shadow-lighter);
    box-shadow: 0 0 0 calc(var(--border-width) * 3) var(--color-shadow-lighter),
    0 0 0 var(--edge-width) var(--color-shadow);
    height: var(--diameter-board);
    margin: calc((100vh - var(--diameter-board)) * 0.5) calc((100vw - var(--diameter-board)) * 0.5);
    position: relative;
    width: var(--diameter-board);
}

.board {
    display: flex;
    flex-direction: column-reverse;
    height: 100%;
    width: 100%;
}

.board .row {
    display: flex;
    height: var(--diameter-tile);
    width: 100%;
}

.perspective-black .board .row {
    flex-direction: row-reverse;
}

.perspective-black .board {
    flex-direction: column;
}

.board .row .tile {
    background-color: currentcolor;
    border: none;
    box-shadow: inset 0 0 0 var(--border-width) var(--color-shadow-lighter);
    display: flex;
    flex-direction: column;
    height: var(--diameter-tile);
    justify-content: space-between;
    padding: 0;
    position: relative;
    transition: background-color 350ms var(--transition-ease);
    width: var(--diameter-tile);
}

.perspective-black .board .row:nth-child(even) .tile:nth-child(odd),
.perspective-black .board .row:nth-child(odd) .tile:nth-child(even),
.perspective-white .board .row:nth-child(even) .tile:nth-child(even),
.perspective-white .board .row:nth-child(odd) .tile:nth-child(odd) {
    color: hsl(var(--color-board-hue), var(--color-board-sat), 62%);
}

.perspective-black .board .row:nth-child(even) .tile:nth-child(even),
.perspective-black .board .row:nth-child(odd) .tile:nth-child(odd),
.perspective-white .board .row:nth-child(even) .tile:nth-child(odd),
.perspective-white .board .row:nth-child(odd) .tile:nth-child(even) {
    color: hsl(var(--color-board-hue), var(--color-board-sat), 70%);
}

.board .row .tile.highlight-active {
}

.board .row .tile.highlight-capture {
}

.board .row .tile.highlight-move {
}

.board .row .tile .move,
.board .row .tile .moves,
.board .row .tile .captures {
    box-sizing: border-box;
    display: flex;
    flex-wrap: wrap;
    height: var(--diameter-tile);
    justify-content: center;
    left: 0;
    padding: calc(var(--diameter-tile) * 0.025);
    position: absolute;
    top: 0;
    width: var(--diameter-tile);
    z-index: 9;
}

.board .row .tile .move,
.board .row .tile .moves {
    align-content: center;
    align-items: center;
}

.board .row .tile .captures {
    align-items: flex-start;
    justify-content: space-between;
}

.board .row .tile:not(.occupied) .captures {
    align-items: center;
    justify-content: center;
}

.board .row .tile > div > svg {
    --stroke: transparent;
    box-sizing: border-box;
    height: var(--di);
    line-height: var(--di);
    width: var(--di);
}

.board .row .tile .move svg {
    --di: calc(var(--diameter-tile) / 4);
    --fill: var(--color-shadow);
}

.board .row .tile .moves svg,
.board .row .tile .captures svg {
    --di: calc(var(--diameter-tile) / 4);
    --fill: var(--color-shadow);
    opacity: 0.4;
}

.board .row .tile.occupied .captures svg {
    position: absolute;
}

.board .row .tile.occupied .captures svg:nth-child(1) {
    top: 0;
    left: 0;
}

.board .row .tile.occupied .captures svg:nth-child(2) {
    top: 0;
    right: 0;
}

.board .row .tile.occupied .captures svg:nth-child(3) {
    bottom: calc(var(--di) * 0.1);
    left: 0;
}

.board .row .tile.occupied .captures svg:nth-child(4) {
    bottom: calc(var(--di) * 0.1);
    right: 0;
}

.board .row .tile.occupied .captures svg:nth-child(5) {
    top: calc(50% - var(--di) * 0.55);
    left: 0;
}

.board .row .tile.occupied .captures svg:nth-child(6) {
    top: calc(50% - var(--di) * 0.55);
    right: 0;
}

.board .row .tile.occupied .captures svg:nth-child(7) {
    top: 0;
    left: calc(50% - var(--di) * 0.5);
}

.board .row .tile.occupied .captures svg:nth-child(8) {
    bottom: calc(var(--di) * 0.1);
    left: calc(50% - var(--di) * 0.5);
}

.touching .board .row .tile .moves,
.touching .board .row .tile .captures,
.turn-black .board .row .tile .moves .white,
.turn-black .board .row .tile .captures .white,
.turn-white .board .row .tile .moves .black,
.turn-white .board .row .tile .captures .black {
    display: none;
}

.board .row .tile[class*="highlight-"] .moves,
.board .row .tile[class*="highlight-"] .captures {
    display: none;
}

button:focus {
    outline: none;
    position: relative;
    z-index: 9;
}

svg {
    --fill: var(--color-black);
    --stroke: var(--color-shadow);
    fill: var(--fill);
}

svg.white {
    --fill: var(--color-white);
}

svg.black {
    --fill: var(--color-black);
}

.pieces {
    display: block;
    height: var(--diameter-board);
    left: 0;
    pointer-events: none;
    position: absolute;
    top: 0;
    width: var(--diameter-board);
    z-index: 99;
}

.pieces .piece.white {
    --pos-row: -1;
}

.pieces .piece.black {
    --pos-row: 8;
}

.pieces .piece {
    --pos-col: 3.5;
    --scale: 0;
    --transition-delay: 0ms;
    --transition-duration: 200ms;
    bottom: 0;
    display: block;
    height: var(--diameter-tile);
    position: absolute;
    left: 0;
    transform: translate(
            calc(var(--pos-col) * 100%),
            calc(var(--pos-row) * -100%)
    ) translateZ(0);
    transform-origin: 50% 50%;
    transition: all var(--transition-duration) var(--transition-ease) var(--transition-delay);
    width: var(--diameter-tile);
}

.perspective-black .pieces .piece {
    transform: translate(
            calc((7 - var(--pos-col)) * 100%),
            calc((7 - var(--pos-row)) * -100%)
    ) translateZ(0);
}

.pieces .piece svg {
    display: block;
    left: 50%;
    opacity: 1;
    position: absolute;
    top: 50%;
    transform: translate(-50%, -50%) translateZ(0) scale(var(--scale));
    transform-origin: 50% 50%;
    transition: transform var(--transition-duration) var(--transition-ease),
    fill var(--transition-duration) var(--transition-ease),
    opacity var(--transition-duration) var(--transition-ease);
}

.turn-white .pieces .piece:not(.highlight-capture) svg.black,
.turn-black .pieces .piece:not(.highlight-capture) svg.white,
.turn-black .pieces .piece:not(.can-move):not(.can-capture) svg.black,
.turn-white .pieces .piece:not(.can-move):not(.can-capture) svg.white {
    --stroke: transparent;
    opacity: 0.8;
}

@keyframes wobble {
    0%, 50%, 100% {
        transform: translate(-50%, -50%) translateZ(0) scale(1) rotate(0deg);
    }
    25% {
        transform: translate(-50%, -50%) translateZ(0) scale(1.1) rotate(-2deg);
    }
    75% {
        transform: translate(-50%, -50%) translateZ(0) scale(1.1) rotate(2deg);
    }
}

.pieces .piece.highlight-active svg {
    animation: wobble 500ms linear infinite;
    --stroke: var(--color-success);
}

.pieces .piece.highlight-capture svg {
    --stroke: var(--color-danger);
}

.piece svg {
    --svg-di: calc(var(--diameter-tile) * 0.666);
    display: block;
    font-weight: bold;
    height: var(--svg-di);
    left: 50%;
    line-height: var(--svg-di);
    position: absolute;
    stroke-linejoin: round;
    text-align: center;
    top: 50%;
    transform: translate(-50%, -50%);
    width: var(--svg-di);
}