I need State to reset whe quantity gets below zero

I have a shopping cart icon, that grows briefly, then shows a number alert with the number if items (this is a different state of the icon with variable number). If you click the plus button, that number increases, and if you click the minus, the number decreases.

When it gets below zero, I want the shopping cart icon to revert to the default state (without the number). I have tried many different conditionals. Everything works, except that it never reverts back to the default state below zero.