@gustavocampos1
The 'Base font size (px)' in the interface goes up to only 16. All values set within the interface should result in a layout that looks OK.
Adding custom CSS can cause knock-on effects that might need to be resolved (as you have discovered).
If you find that your text is not being displayed in its entirety, then you may need to expand the container it is in with further CSS rules.
If the problem you are having is that you are using the Kosel theme and the top of the menu text is disappearing, try adding the following to your '_themes/kosel/css/custom.css' file:
nav ul {
padding-top: 5px;
}
If this does not help, then please post the URL to your web site so that I can take a look and help further.
Incidentally, if you are not already using the current version of Showkase (v1.3.0), you can upgrade following the instructions here.