Comparison slider

JavaScript

const divisor = document.getElementById("divisor"),
        handle = document.getElementById("handle"),
        slider = document.getElementById("slider");

    function moveDivisor() {
        handle.style.left = slider.value+"%";
        divisor.style.width = slider.value+"%";
    }

    window.onload = function() {
        moveDivisor();
    };

Html

<div class="column is-3">
    <div class="container">
        <div id="comparison">
            <figure>
                <div id="handle"></div>
                <div id="divisor"></div>
            </figure>
            <input type="range" min="0" max="100" value="50" id="slider" oninput="moveDivisor()">
        </div>
    </div>
</div>

CSS

.container {
    max-width: 800px;
}

#comparison {
    width: 100%;
    padding-bottom: 100%;
    overflow: hidden;
    position: relative;
}

figure {
    position: absolute;
    background-image: url(https://s3-us-west-2.amazonaws.com/s.cdpn.io/4273/photoshop-face-before.jpg);
    background-size: cover;
    font-size: 0;
    width: 100%;
    height: 100%;
    margin: 0;
}

#divisor {
    background-image: url(https://s3-us-west-2.amazonaws.com/s.cdpn.io/4273/photoshop-face-after.jpg);
    background-size: cover;
    position: absolute;
    width: 50%;
    box-shadow: 0 5px 10px -2px rgba(0, 0, 0, 0.3);
    bottom: 0;
    height: 100%;
}
#divisor::before, #divisor::after {
    content: "";
    position: absolute;
    right: -2px;
    width: 4px;
    height: calc(50% - 25px);
    background: white;
    z-index: 3;
}
#divisor::before {
    top: 0;
    box-shadow: 0 -3px 8px 1px rgba(0, 0, 0, 0.3);
}
#divisor::after {
    bottom: 0;
    box-shadow: 0 3px 8px 1px rgba(0, 0, 0, 0.3);
}

#handle {
    position: absolute;
    height: 50px;
    width: 50px;
    top: 50%;
    left: 50%;
    transform: translateY(-50%) translateX(-50%);
    z-index: 1;
}
#handle::before, #handle::after {
    content: "";
    width: 0;
    height: 0;
    border: 6px inset transparent;
    position: absolute;
    top: 50%;
    margin-top: -6px;
}
#handle::before {
    border-right: 6px solid white;
    left: 50%;
    margin-left: -17px;
}
#handle::after {
    border-left: 6px solid white;
    right: 50%;
    margin-right: -17px;
}

input[type=range] {
    -webkit-appearance: none;
    -moz-appearance: none;
    position: absolute;
    top: 50%;
    left: -25px;
    transform: translateY(-50%);
    background-color: transparent;
    width: calc(100% + 50px);
    z-index: 2;
    cursor: pointer;
}
input[type=range]:focus, input[type=range]:active {
    border: none;
    outline: none;
}

input[type=range]::-webkit-slider-thumb {
    -webkit-appearance: none;
    border: none;
    height: 50px;
    width: 50px;
    border-radius: 50%;
    background: transparent;
    border: 4px solid white;
    box-shadow: 0 0 8px 1px rgba(0, 0, 0, 0.3);
}

input[type=range]::-moz-range-track {
    -moz-appearance: none;
    height: 15px;
    width: 100%;
    background-color: transparent;
    position: relative;
    outline: none;
}