Hi there,
i can see a Rich Text Widget has been used to add the Slider to it.
Part of the sliders code is this HTML Comment:
<p><!-- START Slider 1 REVOLUTION SLIDER 6.2.2 --></p>
Which although is not displayed has 1.5em bottom margin attached to it.
I am not sure if the comment can be removed. If not can you add a CSS Class to the Rich Text Widget eg. remove-margin
Then you can add this CSS:
.remove-margin > p {
margin-bottom: 0 !important;
}
For the naviation – why not set the Customizer > Layout > Primary Navigation — Alignement to center ?