Black stain on plastic

Try hydrogen peroxide.

Have you tried using a Magic Eraser?

Clean paste with a microfiber cloth. I like Bio Cleaner. You can get it off Amazon but I ordered from QVC when they had free shipping for a better deal.

Here are multiple methods you can try:

https://desertoasiscleaners.com/remove-stains-from-plastic/#:~:text=Baking%20soda%20paste%20is%20a%20great%20disinfectant%20that,applying%20with%20a%20moist%20cloth%20to%20the%20container.

Hello. I would consider trying a magic eraser and some toothpaste.

Use a damp toothbrush and a dab of white toothpaste on the brush. Gently brush the stain making the toothpaste foam up. Try a slurry of hydrogen peroxide and baking soda. Coat the stain with it and let it sit till it dries. Wipe off.

If you can't get the stain out could you just paint the shelf to make it blend in?

Hi Janet, here are a few ideas for you to try, Mix equal parts white vinegar and fresh water in a spray bottle for an excellent bathroom cleaner that can be used liberally on showers and tubs. Fully saturate surfaces and let the vinegar solution sit for at least 15 minutes. Wipe clean with a clean, dry microfiber towel.

For Red or Black Stains, Use Baking Soda and Hydrogen Peroxide. Use the brightening power of baking soda and hydrogen peroxide to remove tough red or black stains. Do not use this method on an acrylic tub—it may scratch the surface. Mix two parts baking soda and one part hydrogen peroxide to form a paste.

I would try a magic eraser, they work wonders on stubborn stains!

Krud Cutter works great https://amzn.to/3AzhJUn

Put another jar over the stain and forget it! Or Maybe paint it with a Matt or Satin Paint!

A magic eraser will scratch the surface. Try some gel toilet cleaner.