Right now the list of available buttons in the modeller are all default buttons with a background-fill. It is not possible to select outline buttons. Whenever you'd add btn-outline-primary as a class to a button, it will still use the background color of the selected button class from the modeller and not the transparent one that is added through btn-outline-* classes.
This is due to the fact that Bootstrap 4 is included in our project instead of Bootstrap 3 (see comments).
You are right! We replaced Bootstrap 3 with 4 so that might cause the issue.
Hi Freek, btn-outline is created for Bootstrap 4 that has just been released. Mendix is now using Bootstrap 3, we created the class btn-bordered that has the same effect with Atlas UI.
Have you tried btn-bordered? btn-outline is a bootstrap 4 class and Mendix uses Bootstrap 3