public/assets/maplibre/maplibre-custom-controls.css

.maplibregl-ctrl-split-view {
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 512 512'%3E%3Cpath d='M0 96C0 60.7 28.7 32 64 32H448c35.3 0 64 28.7 64 64V416c0 35.3-28.7 64-64 64H64c-35.3 0-64-28.7-64-64V96zm64 64V416H224V160H64zm384 0H288V416H448V160z'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-size: 20px 20px;
    background-position: 5px 5px;      
}