styles.css

body {
    position: absolute;
    top: 0;
    left: 0;
    margin: 0;
    width: 100vw;
    height: 100vh;
    overflow: hidden;
    font-family: 'Press Start 2P';

    -webkit-user-drag: none;
    user-select: none;
    -moz-user-select: none;
    -webkit-user-select: none;
    -ms-user-select: none;
}

canvas {
    position: absolute;
    top: 0;
    left: 0;
    z-index: -2;
    background-color: #40c4ff;
}

#gui {
    position: absolute;
    left: 0;
    top: 0;
    margin: 10px;
    padding: 0;
    user-select: none;
    opacity: 0;
    max-width: 30%;
}

#gui p {
    padding: 5px;
    margin: 0;
}

#loadingScreen {
    position: absolute;
    top: 0;
    left: 0;
    z-index: 0;
    width: 100vw;
    height: 100vh;
    background-color: #757575;
    text-align: center;
}

.fadeOut {
    animation: fadeOut 1s;
    animation-fill-mode: forwards;
}

.fadeIn {
    animation: fadeIn 1s;
    animation-fill-mode: forwards;
}

@keyframes fadeOut {
    from {
        opacity: 100%;
    }

    to {
        opacity: 0%;
        visibility: hidden;
    }
}

@keyframes fadeIn {
    from {
        opacity: 0%;
    }

    to {
        opacity: 100%;
    }
}