How to make contenteditable not save tags?

Question

css

Such a problem, I have a contenteditable div, and a button that adds a span.bold tag to the selected text, and through css I make it bold (that's exactly what I need), but the problem is that the div remembers that this text is bold, and if erase the text, then the tag is removed, and the new text already appears with the b tag, how to fix this?