To enhance the look&feel in dark theme, I suggest to change renderAction like that:

renderAction: anAction
^(UITheme current 
newButtonIn: nil 
for: anAction
getState: nil
action: #morphicActOn:
arguments: {}
getEnabled: nil
label: (AlphaImageMorph new image: anAction icon)
help: (anAction title, Character tab asString, anAction shortcutAsString) trimBoth)
valueOfProperty: #noBorder ifAbsentPut: [true]; "this is a hack to tell the GLMUITheme to not draw the border and the fill"
valueOfProperty: #noFill ifAbsentPut: [true];
setProperty: #wantsKeyboardFocusNavigation toValue: false; "to disable the focus"
borderWidth: 0;
yourself

basically, just add #borderWidth: 0. It will remove the border (invisible in the regular theme), and then dark theme will behave the same… and it will look a lot better: 


before: 


after: 



cheers, 
Esteban

ps: yes, we still need to play with the icons, but this small step is anyway needed :)