$('#cff .cff-item').first().before( $('#cff_your_post_id').addClass('cff-pinned') );
You’d need to replace the “cff_your_post_id” part in the snippet with the ID of the post you want to pin to the top of your feed. You can find the ID of the post you want to pin by right clicking on it and clicking “Inspect Element”. You should see an ID on the cff-item element as shown below.
To change the styling of the pinned post you can add CSS to the plugin’s Custom CSS section, for example:
border: 1px solid rgba(0,0,0,0.3);
box-shadow: 0 0 10px 0 rgba(0,0,0,0.15);