If you have a custom style for your forum, unfortunatelly it will never be officially supported by the extension. However, that doesn't mean that you can't add support for it yourself.
Adding custom support for Linked Accounts
If you look into the
styles/prosilverdirectory under the Linked Accounts root path you'll see all the necessary files in which you will need to base yourself to add support for your style.
Prosilver-based styles are easier to work with as you will only need to modify the CSS to add the necessary changes (assuming that you didn't modify the navbar's HTML structure). In any case, here's is what you need to know to modify either the CSS of Linked Accounts or any of the templates.
stylesdirectory you'll find a
prosilverfolder with all the style files for Prosilver. To add custom support for any theme you'll need to first create a new directory where the
prosilverfolder is with the same name as your style's directory. If your style is based on Prosilver, you will only need to copy inside your newly created folder the files you are going to modify (respecting the same directory structure) as the others will be inherited. In the opposite case, you'll have to completely copy the prosilver folder and start doing the neccesary modifications to all files.
As it has already been said, in most of the cases where themes are based on prosilver, a simple style folder with a
theme/linkedaccounts.cssfile customized should be sufficient.