Can't access the buttons for custom layers.

Please use these commands:
Right click on the page
Select Inspect Tool
Click Console

Copy Paste this line:
jQuery('#layer-buttons-wrapper > div > div:nth-child(2) > span > button').click();  // For Custom Layers

jQuery('#layer-buttons-wrapper > div > div:nth-child(1) > span > button').click();  // To delete the base layer.

Hit Enter. 

It will enable the custom layers panel / delete the base image.