Steps to reproduce
- create <source style="overflow:auto"> element to make it wrap to its surroundings
- see the weird border not to be seen when using <pre style="overflow:auto">
Expected behavior
overflow:* should not create an extra element making weird border or there should be some other way to specify overflow/flow/positioning directly to the <source>
Current behavior
Currently this together with T29828 are reasons why <source> is still not much used in Czech Wikipedia's documentation pages (ns Help, Project, and doc subpages in ns Template and Module)