@0ffme: Unfortunately, that is the choice of the developer. For ex, I have provided both a normal extension and a sidebar extension, but most others dont provide this.
If you are comfortable with editing extensions, I could instruct you further.

@watersotr said:

I don't understand what this is. what is a workspace? what does this phrase mean, " fine tab counting functionality to Opera GX"? what is a "fine tab"? what does "counting functionality" mean?

Workspaces are a feature of opera gx (and other opera browsers) essential for tab organization.
Fine tab counting functionality means counting the number of tabs at a fine-grained level, i.e. per workspace.

what does this phrase mean, " adding the current workspace's tab count to the badge"? what is "the badge"?

a badge for an extension is the little number/text displayed next to it's icon in the extensions display right of the address bar.

as a matter of fact, every time I have checked to see what various add-ons are, I cannot understand the explanations at all.

You should get accustomed with the features before looking at extensions. Go to opera's home page and click on features to get started (https://www.opera.com/features).

Does your windows explorer window also have white borders around it/ is your windows theme color white?
If so, then it's a windows thing.
Also you shouldn't have a border when running it maximized.