Watch the part where the Grinch is stealing the Christmas gifts and decorations. When he takes the lights and takes off on his rocket-powered sleigh, the lights reappear as if he never stole them!
The Grinch never stole the lights. They were always there. He just killed the electricity. This is a blooper though, and I noticed it in the big screen. They accidently made the lights go back on in the scene right after he killed the power.