antosdk-apps/Booklet/build/debug/main.css

afx-app-window[data-id ='Booklet'] div.editor-toolbar{
    background-color: white;
}

afx-app-window[data-id ='Booklet']  afx-tree-view .afx-tree-view-item:before{
    content: "\f292"; 
    font-family: "FontAwesome";
    font-size: 16px;
    font-style: normal;
    font-weight: normal;
}