Sidewalk theme introduces a specific feature called Highlight Posts. Basically, you can choose any specific post to be “highlighted” and it will be displayed in a different styling (color) than other posts on listing pages.
The main purpose of this feature is to attract visitors attention to specific posts while exploring through the website. It can be useful if you, for example, have some kind of “sponsored” articles on your website or if you just want some important posts to stand out among others for any particular reason.
To set up your highlight posts, just go to Theme Options -> Highlight Posts section as shown in the image below:
Watch an example in this short video: