The responsive design of the Stack Exchange sites affects how the different UI elements/sections are sized, positioned or reflow.
These effects can be seen for different devices, screensizes, portrait/landscape, etc.
Elements/Section that are involved include (but are not limited to):
- Topbar elements (search bar, usercard)
- left bar (navigation, teams (on Stack Overflow only))
- right bar (with the meta questions and ads)
- main content
When reporting bugs include browser make and version, screensize, zooming and if it involves dynamic behavior consider making an animated GIF to showcase the issue.