Option garbage CSS testcase

Expected behavior for below pull-down list: Garbage is not displayed.
M5 actual behavior: Garbage from other parts of the page or other windows appears.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.
This text is here to create a scrollbar.