Use Goo Gone, not alcohol.

Goo Gone works best for this kind of rubber-to-mousepad adhesive residue. Rubbing alcohol can dry out or warp the mousepad’s rubber base, especially on cheaper pads. A few drops of Goo Gone, a rag, and some elbow grease will lift it off without damaging the surface.

If you don’t have Goo Gone, cooking oil (olive or vegetable) will also work in a pinch. Same method: apply, let it sit a minute, then wipe. Just don’t use acetone or nail polish remover—that will definitely melt the rubber.

Wash the area with mild soap and water after to remove any oily residue, and let it fully dry before using the mousepad again.