In the select directory dialogs (e.g. Settings -> Files -> Directories -> Select directory), the OK and Cancel buttons are shown without outlining, only the text is visible.
The file dialogs (save as etc.), seems to be OK.

This seems to look fine. Can you let me know which style you are using (Preferences > User Interface > Appearance > Dark Style)?

Color theme mode = Auto, Dark style = Glow. This is the default setting from when I installed.
My windows setting is dark style (it says in italics)

In beta 2, this gives a run-time exception. Mail with elf file sent to support

We'll check it out.

Update: it seems that still only the button text is displayed, and no 3D effect on buttons, just a dotted white outlining when "button" is pressed

Solved in beta 3, but there is a visual disturbing white background screen when the folder browser window is opened. This also goes for e.g. the Recall popup in SQL window, properties and describe window for tables etc. It looks as if a light theme is applied as default before the application (in a split-second after) decides to use the dark theme.

It's a Windows dialog, so I'm not sure if this can be fixed. We'll look into it though.