When using, for example, a RadzenRequiredValidator with Popup set to true, the message in a lot of cases will show up behind other controls on the screen. I have been solving this from project to project via adding z-index to rz-message-popup in my app.css:
.rz-message-popup {
z-index: 99;
}
Seems like the rz-message-popup css should have some level of higher z-index applied to it by default, since apart from maybe a few edge cases, we would want it to be on top of everything else as it is a "popup".
All that said, 99 might not be the best choice for the Radzen library. 99 works for my limited use cases, but I am not immune to the fact that for example these popups when scrolled shouldn't obfuscate sticky things like page headers/footers, so maybe something a bit lower as a default starting point would be better.