html, body, .clock-div, .digit, .bit {
    display: flex;
}

html, body {
    height: 100%;
    width: 100%;
}

.clock-div {
    flex: 1 1 auto;
    border: 2px solid black;
    z-index: 2;
}

.digit {
    flex: 1 1 auto;
    flex-direction: column;
}

.bit {
    border: 2px solid black;
    flex: 1 1 2px;
    text-align: center;
}

.bit.on {
    background: white;
    color: white;
}

.bit.off {
    background: black;
    color: black;
}

.clock-canvas {
    display: none;
    z-index: -1;
}
html, body, .clock-div, .digit, .bit {
    display: flex;
}

html, body {
    height: 100%;
    width: 100%;
}

.clock-div {
    flex: 1 1 auto;
    border: 2px solid black;
    z-index: 2;
}

.digit {
    flex: 1 1 auto;
    flex-direction: column;
}

.bit {
    border: 2px solid black;
    flex: 1 1 2px;
    text-align: center;
}

.bit.on {
    background: white;
    color: white;
}

.bit.off {
    background: black;
    color: black;
}

Remove irrelevant selector, all styling is done by JS.
Remove irrelevant selector, all styling is done by JS.
