Hello @RalphT,
I agree with @ScottShearer in that the appearance is related to the theme used in Outlook, and the UI mechanism for button here is that the color is not filled until the mouse arrow is over the button.

When the mouse arrow is over the button:
If you want the submit button to stand out, it is recommended that you change your theme and select the one you like.


Best Regards,
Community Support Team _ Lin Tu
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.