Updated background_color examples to match GTK4 css style format

[mrsteve0924]

i updated the wiki
https://github.com/WayfireWM/wf-shell/wiki/wf%E2%80%90panel#background_color

[trigg]

Good idea to update the docs, but there could be a fair bit more information here. I don't know how much we'd want to cover manually and how much we could point to outside docs for.

https://www.w3.org/TR/css-color-5/

essentially:

• Three digit hex codes : #RGB
• Four : #RGBA
• Six : #RRGGBB
• Eight : # RRGGBBAA
• rgb() / rgba()
• hsl() / hsla()
• hwb()
• named colors (red, dimgray, coral, wheat)

added: also gtk_headerbar is now non-functional and just uses window colour, as there was no way to poll current theme colours out that I could find

[mrsteve0924]

there is certainly a lot of information at that link. I can re-word the wiki update to maybe not give the impression that I am showing all the possible rules. And then include that link too.

so if no background_color is set (or set incorrectly) it will default to window color. no need for background_color=gtk_headerbar.

[mrsteve0924]

i removed the lines that referred to formats and just left the updated examples

[trigg]

Thanks for the help !