[Lazarus] TBitBtn image, how to make background transparent?

[Ondrej Pokorny]

On 13.05.2019 22:36, Bo Berglund via lazarus wrote:
> I am trying to make a bitmap image for a TBitBtn button such that the
> background of the image will be transpoarent and therefore the button
> color will be visible.

What OS and WidgetSet? If you are on win32 - AFAIR a PNG works just fine.

Ondrej