antosdk-apps/RemoteDesktop/assets/main.css

afx-app-window[data-id="RemoteDesktop"] div[data-id="container"]
{
    background-color: #272822;
}
afx-app-window[data-id="RemoteDesktop"] canvas[data-id="screen"]
{
    border:0;
    margin: auto;
    display: block;
}