1.Material UI allows overriding CSS of their elements. Have you tried? We've done such overriding so in Navigation.js.
I think you could take a look here https://material-ui.com/customization/overrides/

2.I expect this to change, but
a) I think position: absolute and float: right don't work together
b) I can see that actually position: absolute is overwritten by some inline properties that maybe that react component adds.

3.I suggest to stick to either uppercase, or lowercase for hex values.[Да се провери дали сме го оправили навсякъде]

4.keep margin and padding properties together (move this one up), remove whitespace.
This is more of a general note, I expect these might change once you switch to material UI input.[И това също]

5.Why don't you use css's :hover instead, set display: none as a default value in the class and then have display: block in the :hover class?[Не ми стигнаха силитие да го оправя]

6.Is there a reason why you are not using material ui's toggle? It would generally be better to use components from material ui.[Евентуално да пробваме да видим дали не можем да го направим с Material UI даже и да не изглежда така]