.menu-collapsed-mode li[data-top-menu-id="top_menu_id_knowledgebase"] .menu-item-icon {
    background-image: url("/bitrix/images/ithive.knowledgebase/knowledgebase_icon_menu_dark.svg");
    font-size: 0;
}
.bitrix24-default-theme .menu-collapsed-mode li[data-top-menu-id="top_menu_id_knowledgebase"] .menu-item-icon {
    background-image: url("/bitrix/images/ithive.knowledgebase/knowledgebase_icon_menu_light.svg");
    font-size: 0;
}