Revert "Use reversed tilde for "Seealso""

This reverts commit a4131fdc97db70e915a13bf8a74b2f20feb6ce52.
Revert "Use three asterisms for `hr`"

This reverts commit 9587d0de670725892b6143c9b3a3b294f5e5236a.
Remove unnecessary variables and line breaks
Fix variable name for `dd` of "Flat DL"
Use `rgb()` notation for colors
Refer parent bgcolor instead of `white`
Add `mark` fg color
Fix property order
Remove unnecessary properties
Use variables as possible
Version 6.51.1