::after pseudo-element is not shown

[CYBAI]

We can click the checkbox to change the style of the div but we cannot see the circle created by ::after on Servo.

<style>
input[type=checkbox]:enabled:checked + div {
    background-color: #0b2b50;
}

div {
    width: 36px;
    height: 20px;
    position: relative;
    background-color: #fafafa;
    border: #e6e6e6 solid 1px;
    border-radius: 19px;
    content: '';
    display: block;
    visibility: visible;
}

input[type=checkbox]:checked + div::after {
    left: 18px;
}

input[type=checkbox]:enabled + div::after {
  box-shadow: 0 2px 4px 0 rgba(0,0,0,0.1);
}

div::after {
    position: absolute;
    top: 2px;
    left: 2px;
    width: 16px;
    height: 16px;
    background-color: #fff;
    border-radius: 100%;
    content: '';
    display: block;
    transition: left 0.15s ease-out, box-shadow 0.15s ease-in-out;
    visibility: visible;
}
</style>

<input type="checkbox" checked />
<div></div>

cc @emilio

Tested with master (5cfc434) on macOS 10.14.3