whoa ThickFrames (for WoW Classic)
Simple and Beautiful mod based for Player and Target frames with fat HP bars an Class colors but still very close to the original Blizzard UI style.
Also check out whoaUnitFrames (for WoW Classic).
NOTE V1.3: There is an issue when upgrading to v1.3.
OPTION 1: Type /wuf in game chat, enable then disable "dark frames" and restart the game.
OPTION 2: Close the game and delete any whoaUnitFrames or whoaThickFrames files in WTF folder and restart game.