Is there a way to create a horizontal form in marketo with 4 columns? (see attached image) I have nested the elements next to each other, however when I go into my guided landing page and insert the form into a full width area it still stacks as a single column form. Would I need to manipulate this form within the form itself or within the landing page to get it to show up correctly or some other way?
Marketo certainly supports multi-column forms — as you're showing here.
You can test the native styles easily by putting the embed on an otherwise empty page (no other CSS at all).
The container element, though, can easily constrain the form so that it doesn't span the page. You have to look at the rest of the contributing CSS styles.
Also, a 5-up form like you have here is simply not practical. It would work for me, because I happen to run at 2560 x 1600, but when you see people's real-world desktop resolutions you'll see it's still a 960 world.
I'll usually add the styles for my forms at the template level using a stylesheet so it's easy to update and global (all pages on the template will have the same set of form styles). Another way you could do this would be to put the CSS in the "Custom CSS" in the form editor to make the styles more form-specific. In this way, they'd "travel with the form" no matter which page it landed on. As a word of caution (and why I prefer the stylesheet approach) - adding local CSS to your forms will clash with any CSS coming from your template or website, etc (wherever the form shows up). Sometimes this is a good thing and other times it's a spaghetti mess of overlapping CSS.
Here's a link to another post with some CSS form stuff in it from a while back - this probably less relevant but it contains some info for context: https://nation.marketo.com/t5/Product-Discussions/Fluid-Responsive-Marketo-Form-CSS/m-p/114059#M7368...
In that thread, you'll find a link Courtney posted to some CSS she's shared that's setup for multi-column CSS. Right now it looks like it's setup to handle up-to 3 columns, but this could be extended up to 5 columns (or more) with a little add'l css. Here's the link she posted for reference: https://gist.github.com/cougrimes/5168524fd9365eedea16