How to left align form Close button

I’ve noticed that my pop-up forms have the CLOSE button on the left sometimes and on the right sometimes. I don’t understand why or how I can force left alignment right under the SAVE button default position. Do I need some simple CSS with a float:left, or do I need javascript, or is there a setting somewhere I am not seeing? Thank you.

Just responding here in case this happens to anyone else in the future. The cause was an incomplete icon tag placed in the Popup Title.

Wow. Thanks, Chem. The icon rendered properly. I never thought to look for a typo there, but sure enough, that was the difference between those right- and left-aligned.