Please Help With Basic PHP

I am a total newbie to this coding stuff, though I have been working online for a couple years ago, this is my first developer project and it is seemingly more difficult then expected, I see why they have “themes” but this client wants specific customization. Anybody who can assist with the following will be much appreciated. Thank you in advance!

WP Template: Blank Slate by Tidy Theme

Inspect Element shows this code for the div.menu 1351px x 160px which needs to be removed:

<div class=”menu”>…</div>

I also need the buttons located in div#container
( Code: div id=”container”>…</div> )

to be in-line block margined 5-10 px apart and center aligned

buttons are located with shortcode wrapped in php in the Header file

For what might be an easy adjustment for someone with technical experience, you might be able to tell me if there is a way in the plugin to possibly edit the parameters without directly editing the code. Maxbuttons is the plugin. or possibly let me know what kind of code to add to the header php file.

Your assistance is greatly appreciated. Thank you