solidity/docs/_static/css/toggle.css

input[type=checkbox] {
    visibility: hidden;
    height: 0;
    width: 0;
    margin: 0;
}

.rst-versions .rst-current-version {
    padding: 10px;
    display: flex;
    justify-content: space-between;
}

.rst-versions .rst-current-version .fa-book,
.rst-versions .rst-current-version .fa-v,
.rst-versions .rst-current-version .fa-caret-down {
    height: 24px;
    line-height: 24px;
    vertical-align: middle;
}

.rst-versions .rst-current-version .fa-element {
    width: 80px;
    text-align: center;
}

.rst-versions .rst-current-version .fa-book {
    text-align: left;
}

.rst-versions .rst-current-version .fa-v {
    color: #27AE60;
    text-align: right;
}

label {
    margin: 0 auto;
    display: inline-block;
    justify-content: center;
    align-items: right;
    border-radius: 100px;
    position: relative;
    cursor: pointer;
    text-indent: -9999px;
    width: 50px;
    height: 21px;
    background: #000;
}

label:after {
    border-radius: 50%;
    position: absolute;
    content: '';
    background: #fff;
    width: 15px;
    height: 15px;
    top: 3px;
    left: 3px;
    transition: ease-in-out 200ms;
}

input:checked+label {
    background: #3a7ca8;
}

input:checked+label:after {
    left: calc(100% - 5px);
    transform: translateX(-100%);
}

html.transition,
html.transition *,
html.transition *:before,
html.transition *:after {
    transition: ease-in-out 200ms !important;
    transition-delay: 0 !important;
}

nav.wy-nav-side {
    /* The default padding of 2em is too small and the "Keyword Index" link gets obscured
     * by the version toggle. */
    padding-bottom: 3em;
}