Removing `0.8em` VE special base `font-size` for UI as we're unifying
OOUI interfaces to `14px` equals to `0.875em` at user agent default size.
Bug: T97631
Depends-on: I693d168d2ccf2babbcfe8952af3e1c262aa97773
Change-Id: I84edeec38ecfb90f5d53199f3b26fc3f83ab0611