I have some experience of the Stylish site.

What is it exactly you wanted to know ?

You could try the following.

Go to this particular page.
Valacar

There you will see that there is someone who wanted to modify Valacar's Logo.

You can see at the top of the page Valacar's typically generous response.

You may be able to follow up on that response by downloading the files he refers to and hence learn something useful.

Had you thought also of maybe using the structure of one of Valacar's Google Styles and cutting and pasting the base64 version of your own image in the place of his ?

If you had any questions you could also perhaps at a later date try contacting Valacar on his own Webpage

I don't think you could find a better mentor.

You probably have your own base64 Encoder, but there is one on line. If you wanted I could search it out for you.

I know that you know of Valacar, and that you have even made a logo based on his Style.

I hope nevertheless that you are not too disappointed by my suggestions.

I am glad that worked.

I found this with a quick search on the Userstyles site.

Maybe you could make something with it.

Favicon

I'll get back to you about the decoder

Good I am glad that worked.

A question for you.

How do you post an image on this site so that you have a small image which can expand to a big one ?

I don't know how to do that.

Thanks for your quick reply.
I prefer myself to use Picamatic.
But the process is probably similar.

This is a Binary File to Base64 Encoder that you may find useful.

Was not able to lay my hands so far on a suitable Decoder.