Add a border and background color to a text block in 7.1

Using Squarespace 7.1, I'd like to put a border with a thin line around a text blocks. Or around a poster image or any image block that has text and a button in it. Can someone help with the CSS on this?

Like this and if possible a different selected background color.

Thanks!

You can use this code

#block-id {
	border: 1px solid black;
}

Use this tool to find block id. https://chrome.google.com/webstore/detail/squarespace-id-finder/igjamfnifnkmecjidfbdipieoaeghcff?hl=en