Question

How do I prevent this overflow?

Answer 1

Rather than wrapping overly long tag names I would recommend limiting the maximum length of tag names. You can so so with the Tagging Tools plugin.

Comments

thank you this was very helpful for me

Answer 2

Add this css 

.qa-sidepanel {

    word-wrap: break-word;

}

Comments

Word-wrap here should be applied to tag names.