Page templates, no bold text

In the text editor when I change my text to bold on the preview it won’t change, it’s just plain text. This happens with my default template and the one I set up.

I’m not sure if the css is not linked into the php document (not sure how to do that) or that I need to change the style.css.

Help, please?

[No bumping. If it’s that urgent, consider hiring someone.]