Lines between course sections (topics) do not go all the way across the screen for some topics in Chrome browser unless you're in a full screen 100% zoom. If you start to zoom in or out, the lines will disappear or shift into a second row. https://www.screencast.com/t/1FVyAA1WkB0

1. Create a new course or use an existing course.
2. Change the course format to collapsed topics
3. If you have color shaded boxes, then you may need to revert that setting to "ffffff" https://www.screencast.com/t/YiuKnVC4QY Go to course edit settings>course format> scroll down till you see "toggle background" and "toggle background hover" This does not have to be changed but it is easier to see the lines if the boxes are white. 
4. Go to the course and be sure the tabs are closed. Zoom in and out of the page and observe the lines not going all the way across to divide the section or at time doubling. 

This only happens in Chrome and with collapsed topics. Boost and classic theme show the same thing.