You can change an icon for a widget tab by applying the CSS rule.
For example, if you have added a new tab with name “favorites”, then you can add the following code:
.uploadcare-dialog-tab-favorites:before {
background-image: url(https://your_sprite.png) !important;
background-position: 0 50px;
}
.uploadcare-dialog-selected-tab.uploadcare-dialog-tab-favorites:before {
background-position: 0 0;
}
https://your_sprite.png
should be a 100×200 image with active and inactive states.
The same way you can customize icons for standard tabs.