With the idea of writing more in 2018, being able to display code blocks that are legible and functional is important.
Adding a screenshot may well be the quickest way to display code to a post but it's not the best approach. Code can't be copied and used from a picture, so this approach is pretty much useless for the reader.
On Steemit, simply highlight the text with your cursor and hit the curly bracket ( { ) in the nav.
I've had a couple of issues with spacing when editing the code in this state so write everything in your editor of choice and paste it in as a last step.