Revert "More cleanup of SASS stylesheets. The SASS is admittedly very simple,"

This reverts commit 882738f3363fc17722e4181806c9b4379c6e4756.
Revert "Rename theme showcase from preseed to inventory layout."

This reverts commit b5710c1f4b4abb5c35fb2b579c103d22c0e144d5.