This pack fixes the top of sandstone and red sandstone walls to be connected to the top of regular sandstone and red sandstone. In the default resource pack, the top texture of these walls is simply a flipped over sandstone block, but in this pack, they have been improved to use the top of the block for the top of the walls.
Here you can see how the walls look in use with the Faithful Resource Pack, which this pack was originally made to be an add-on for. However, this will work in any resource pack, including default.
OptiFine is not required.