I use a skinning mod called
Aurora. It reskins all the blizzard frames in the game. But it modifies the frames itself instead of just altering the original artwork.
Because of this, stuff like the login screen and such are untouched and look out of place. Fortunately, there is a fix for that. It's called
Aurora Missing Textures. It replaces the original blizzard style UI art with stuff that matches Aurora. So on the login screen and character select screen you get this.
Just remember that Aurora Missing textures replaces the blizzard artwork, so it will effect everything in the game. If you use Aurora Missing Textures without using Aurora, things may look a bit off. Hope this is the information you were looking for. If not, sorry.