text container draw outside browser window / 100% wrapper

hello!

I’m apologizing for my bad vocabulary regarding webdesign in advance and I hope someone understands my problem and can help me!

I’m currently setting media queries for my website and when I reach 660px window width, I want my containers/posts to have 100% width. problem is that the text draws outside the container/vanishes behind the border of the browser window. firefox tells me the box is about 700px wide although the window is only 660 px wide. I looked for other elements on the website being bigger than the window but I couldn’t find anything … plus the wrapper is also 100%, being as wide as the window.

I’d be so glad if someone could help me, I tried lots of stuff but nothing works … (eg. setting the container width to max-width:660px)

thank you!