Qazi,
Just add these rules to [install dir]\server\apps\[app#]\themes\TabTheme\common.css
.jimu-widget-onscreen-icon {
position: absolute;
cursor: pointer;
border-radius: 4px;
background-color: rgb(0, 0, 0);
-ms-filter: "Alpha(opacity=80)";
background-color: rgba(0, 0, 0, 0.7);
}
.jimu-widget-onscreen-icon.jimu-state-selected {
background-color: rgb(0, 0, 0);
-ms-filter: "Alpha(opacity=100)";
background-color: rgba(0, 0, 0, 1);
}
.jimu-widget-onscreen-icon:hover{
background-color: rgb(0, 0, 0);
-ms-filter: "Alpha(opacity=85)";
background-color: rgba(0, 0, 0, 0.85);
}