I just wanted to expand on the response from @BenM based on what I read here from Ire Aderinokun. Because the user-agent stylesheet provides helpful default styling, think twice before overriding it.
I had a dumb error where a button element didn’t look right in Chrome. I had partially styled it because I didn’t want it to look like a traditional button. However, I left out style elements like border, border-color, etc. So Chrome was stepping in to supply the parts that it thought I was missing.
The problem went away once I added styles like
border: none, etc.
So if anyone else is having this problem, make sure you are explicitly overriding all the applicable default user-agent styles for an element if you notice it looks wonky, especially if you don’t want to reset the user agent styles completely. It worked for me.