main.css

body {
    margin: 0;
    padding: 0;

    font-family: sans-serif;
}

#game_container {
    display: grid;
    grid-template-rows: auto max-content;
    grid-template-columns: auto;
    grid-template-areas:
        "map"
        "controls";

    background: black;
    width: 100vw;
    height: 100vh;
}

#game_map {
    grid-area: map;

    /* When combined with "position: absolute;" in the canvas,
     * this makes canvas sizing work correctly. */
    position: relative;
}

#game_canvas {
    position: absolute;
    width: 100%;
    height: 100%;
}

#game_overlay {
    position: absolute;
    left: 1em;
    top: 1em;

    background-color: rgb(60, 255, 0);
    border: 2px solid rgb(28, 121, 0);
    border-radius: 0.5em;
    font-size: 16pt;
    padding: 0.5em;
}

#game_overlay:empty {
    display: none;
}

#game_controls {
    grid-area: controls;

    display: flex;

    padding-left: 1em;
    padding-right: 1em;
    padding-top: 0.3em;
    padding-bottom: 0.3em;
    align-items: center;

    background-color: #555;
    font-family: "Courier New", "Liberation Mono", monospace;
    font-size: 16pt;
}

#game_controls > * {
    height: 100%;
    margin-right: 0.5em;
}

#game_controls label {
    padding-left: 0.5em;
    border-radius: 3px;

    color: white;
    background-color: #777;
}

#game_controls label#current_player {
    display: flex;
    align-items: center;
    padding-right: 0.5em;
}

#game_controls label#current_player:empty {
    display: none;
}

#game_controls label#current_player:before {
    background-color: var(--player-color);
    content: "";
    display: inline-block;
    margin-right: 0.5em;
    width: 1em;
    height: 1em;
    border-radius: 0.5em;
    vertical-align: middle;
}

#game_controls input {
    font-family: inherit;
    font-size: inherit;
    padding: 0.2em;
}

#game_controls input[type=number] {
    border: 1px solid #333;
    border-radius: 3px;
    background-color: #eee;

    text-align: right;
}

#game_controls input[type=number]:focus {
    border-color: rgb(0, 174, 255);
}

#game_controls input[type=number]:invalid {
    border-color: rgb(255, 102, 0);
}

#game_controls input[type=number][disabled] {
    background-color: #999;
}

#game_controls input[type=submit] {
    padding-left: 0.5em;
    padding-right: 0.5em;
    border-radius: 3px;

    border: 1px solid #333;
    background-color: rgb(255, 102, 0);
}