I was leaving a comment on an accepted answer, and I noticed that the "add comment" button was overflowing, as was some of the text of the comments.
(I am using Chromium 61.0.3163.100 on Arch Linux 64bit, any additional technical details will be added on demand.)
(Added after Stefan Kohl's comment)
Using Firefox there is no text of button overflow, but it is clear that something is wrong:
Here is a screen shot from Firefox on Android (Nexus 6p) in "full site" mode, while there is no overflow (even the separating lines), something is obviously wrong,for example the separator lines reach all the way to the end of the colored region, while before the add comment dialog is open, they don't.