@khuuvin, you can can decrease the margin distance of the H1 tag by inputting a negative bottom margin in your H1 tag. If the required change is specific to one section then the code below requires additional targeting. The code applies to all your site H1 tags. You'd need to identify the page section first.
For all H1 tags on your site:
For distance between paragraphs - excluding the first P1 to H1 for the whole site: (change the em's or input by px)
If you have Facebook Account Admin Access Facebook should allow you to generate the required Event Page code (see link below). Back In Squarespace, add an 'Embed' Block to a page. In the 'Embed' Editor hit the '<>'on the right-hand side. Copy and Paste the code from FB to the 'Embed' editor. Click set. You may get a message saying something like 'live stream not available in Edit mode', so hit save. And I'd expect the Facebook feed to be on your page. If I'm overlooking something let me know. It's a good idea.