Box shadow for call out boxes

Sorry if this is a double post. I can’t see my previous topic.

I am using Call To Action boxes on my website http://www.capilots.com due to them being able to contain a title, paragraphs and buttons in a visually appealing way.

Question: I would like to add a subtle box border shadow. What CSS code do I need?

Subtle box shadows like shown in this link (points 3. & 4.) https://medium.com/refactoring-ui/7-practical-tips-for-cheating-at-design-40c736799886

Thank you in advance.
Greg