It's very dependent on the theme you use. It'll either be a setting or you'll need to write some CSS.

ok, I'm using the tesseract theme if that helps.

#primary {min-height: 100vh}

You can edit that out of the css.

removing that from the css file screws uo the formatting of the site. any other ideas?

going back into the page builder puts the page back to how it was before i altered the css file but that line of code is still removed from the css file.

Looks like the "fl-row-content-wrap" CSS class.

It has margin-top set to 30px, try 0px instead.

It might not actually be in the css, it is css augmented with js like many responsive designs these days.

Sorry the last time I touched this kind of stuff was when mootools (and IE6) was still a thing and so much has changed.

In the theme options is there a place to put override CSS? Many themes have this now.

Other option may be a child theme.

Also, FYI - I get a 404 from all your top menu links

Child theme is the way to go with wordpress templates. Makes it far easier to update the theme in the future. If not you can lose all your changes and you have to reapply them again. Wordpress websites can be a PITA with updating, and themes and plugins breaking, and developers not updating the plugins for newer versions.

I also noticed that the site is very slow, maybe some really large images loading, or it hasn't been optimised. The text and menu items also aren't easy to read, with blue on a grey background.

The images on the front page are HUGE. Scaling the images before you upload them is probably a good idea, or using the scaled versions that WordPress generates when you upload an image to the media library.

mattwnz:

 

The text and menu items also aren't easy to read, with blue on a grey background.

 

Yes, I would agree with that too.