Is your feature request related to a problem? If so, please describe.
No.

Describe the solution you'd like.
I think the Dragonflight close button art doesnt really fit the AddOn and I would like to see the pre 10.x close button added.
All you have to do is:
in frame.lua under "f.CloseButton:SetScript('OnClick', function() Addon.Frames:Hide(f.id, true) end)" place:
f.CloseButton:SetSize(32, 32)
f.CloseButton:SetDisabledTexture("Interface/Buttons/UI-Panel-MinimizeButton-Disabled")
f.CloseButton:SetNormalTexture("Interface/Buttons/UI-Panel-MinimizeButton-Up")
f.CloseButton:SetPushedTexture("Interface/Buttons/UI-Panel-MinimizeButton-Down")
f.CloseButton:SetHighlightTexture("Interface/Buttons/UI-Panel-MinimizeButton-Highlight")

Describe other alternatives you've considered.
None.

Any additional context?
Screenshot of the closebutton with the code above