Edit in JSFiddle

.dark {
    background: #343c45;
    display: inline-block;
    border: 1px solid black;
}

.light {
    background: #f0f1f2;
    display: inline-block;
    border: 1px solid #aaaaaa;
}

a {
    width: 20px;
    height: 20px;
    background-size: 20px 20px;
    display: block;
    font-size: 0;
}

.light a {
    filter: invert(1);
    -webkit-filter: invert(1);
}

a:first-child {
    background-image: url(http://mdibaiee.github.io/CSS-Filter-Tooltip/close@2x.png);
}
a:last-child {
    background-image: url(http://mdibaiee.github.io/CSS-Filter-Tooltip/add.svg);
}