Revert "Merge pull request #25436 from janus926/bug-1087905"

This reverts commit 64f4a6fa02e16140e005b3ec1195c90a6a698aeb, reversing
changes made to bfbd561aff39154d65ef9891ce3f8bc9e9c5e44c.
Bug 1087905 - Limit the scope of sound_manager.css to avoid affecting #windows div with :nth-last-child(). r=alive