How can I remove white space above sub nav with plain CSS?

See more:

CSS

HTML5

I have made a test nav and a sub nav, Where my problem starts.

The test you can access at: mqxy3km25x - CodeSandbox[^]

Css only would be highly appreciated if not vanilla js should be ok to.

Every help is appreciated.

What I have tried:

I've tried to use,

position: fixed; with top: 0;

Which obv won't work because it shouldn't be focused at 0 px from top and 

position: sticky; 

which doesn't work either.