Change Margins for Standard Separtor – via CSS for mobile

Hey christina,
There are a few different separators so I will try to help with a standard one, and I will assume that you mean smaller than a tablet when you refer to mobile. In this case please try this code in the General Styling > Quick CSS field or in the WordPress > Customize > Additional CSS field:

@media only screen and (max-width: 767px) { 
.hr.hr-default {
	margin: 10px 0 !important; 
}
}

Please adjust the margin to suit and then clear your browser cache and check.
If this doesn’t help please include the url to the page in question so we can take a closer look.

Best regards,
Mike