html/_static/stickysidebar.css

/**
 * Sphinx Doc Design -- Sticky sidebar Overrides
 */

div.sphinxsidebar {
    top: 30px;
    left: 0px;
    position: fixed;
    margin: 0;
    float: none;
}

div.related {
    position: fixed;
}

div.documentwrapper {
    margin-top: 30px;
}