extra </div> tag is being added when content changed

I’m a novice user, so sorry if this is basic. I’ve got a page that I want to change every day. If I even click on the visual mode of my home page, I get an added </div> tag added at the end of the html code, which messes up the white hairline border I have on my homepage. I’d prefer to do basic edits in visual mode, rather than html without worrying about extra things being added. Link to page: https://www.artsandcreativities.com/

What am I doing wrong?