The main mistake you can make when styling layers like text or button is – usage of TinyMCE editor and html tags.
You see, back-end and front-end styles differ and your layer will look also different in both modes. That’s why we strongly recommend to style text objects and other layers with Visual Style Editor to get desired result.
First of all make sure you do not have any tags applied to certain layer. Then switch to Style tab and open Visual Style Editor.