+/* Only show the checkbox when the source is hovered over, is selected, or if it
+ * is not checked. */
+.side-menu-widget-item:hover > .side-menu-widget-item-checkbox,
+.side-menu-widget-item.selected > .side-menu-widget-item-checkbox,
+.side-menu-widget-item-checkbox:not([checked]) {
+ opacity: 1;
+ transition: opacity .15s ease-out 0s;