Wpf, style is not being applied

Question

I\'ve written a user control with popup, who\'s content is being set outside the control. The ControlTemplate of that control looks like the following:

Answer 1

Had a similar issue caused by another problem:

There is a strange bug in WPF that prevents styles, defined in merged dictionaries, from being applied to the first element:

https://www.engineeringsolutions.de/wpf-fix-style-is-only-applied-to-first-element/