How do you resize an embed block?

Hi --

I'd like to embed Instagram posts on a blank page on my website, but when the posts populate, they're huge. I'd like to make them smaller. What's the best way to go about resizing embed blocks? 

The website URL is kendallworman.co/instagram-inspo -- you'll see on IG embed block there currently.

You can add this to Website Tools (under Not Linked) > Custom CSS to resize it

iframe#instagram-embed-0 {
    max-width: 300px !important;
}