How are we supposed to override the classes with custom styles if random numbers keep being added to every class? Am I missing something?

I'm working on a project running MUI 4 and I'm struggling to override the styles of some of the components.

Attached here is one component that I wish to override. In error state, the outline/border of the text field and the legend (the label that shrinks to the top left of the notched outline) is in default red color and I wish to override and change them to a different color.

https://i.sstatic.net/jyMcAIBF.png

Some guidance would be very much appreciated.