Sorry to keep finding these. This is in regards to the Back To Top module ( https://www.drupal.org/project/back_to_top → ).
This time the W3CSS subtheme is preventing any of the CSS color settings to be made to the button image (background, border, hover and text). The default grey that comes with the W3CSS theme still remains. After installing and implementing the Back To Top module, changes to its color settings are made at: Home -> Administration -> Configuration -> User interface -> Back to Top.
As I had already added a definition for "w3-button:hover" in the style.css file in the applicable subtheme folder and that worked for all of the other areas on my site, I suspect Back to Top uses other css definitions. So I am not sure if the subtheme is overriding them (as per the "required field indicator" issue I opened yesterday which you fixed), or additional definitions need to be added to style.css and the standard configuration page for the module does not apply when using the subtheme.
Fixed
1.0
Code
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It's likely this issue predates Contrib.social: some issue and comment data are missing.