index.css

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

#main-canvas {
    display: block;
    width: 100%;
    height: 100%;
}

#file-modal-back {
    display: none;
    position: absolute;
    top: 0; bottom: 0;
    left: 0; right: 0;
    background-color: rgba(0,0,0,0.2);
}

#file-modal-close {
    position: absolute;
    right: 10px;
    top: 5px;
    color: black;
    font-size: 2em;
    transition: .3s ease;
}

#file-modal-close:hover {
    cursor: pointer;
    color: orangered;
    transform: scale(1.1);
}

#file-modal {
    text-align: center;
    background-color: white;
    width: 60%;
    margin: 25px auto;
    padding: 25px;
    border-radius: 5px;
}

#file-modal h3 {
    font-size: 2em;
    font-family: sans-serif;
    font-weight: lighter;
    letter-spacing: 3px;
    margin: 0;
    margin-top: 12.5px;
    margin-bottom: 22.5px;
}

#file-in {
    display: none;
}

#file-in-but {
    margin: 0;
    padding: 5px 12.5px;
    border-radius: 5px;
    border: 2px solid thistle;
    background-color: rgba(0,0,0,0);
    font-family: monospace;
    font-size: 1.25em;
    transition: .3s ease;
}

#file-in-but:hover {
    cursor: pointer;
    transform: scale(1.05);
}

input:focus, button:focus {
    outline: none !important;
}