Currently, all actionable buttons in the Assignments tool are styled the same, with blue background and white text. This makes it difficult to scan through and identify the primary action (e.g., "Post" or "Submit"), as all of the buttons look the same.
We recommend following the approach used by Google and other apps, wherein the "primary" action is styled with a background color, and all other actions (Cancel, Save Draft, navigation between submissions, etc.) be styled in a light grey so as to be less attention-grabbing.
For examples, see the current assignments submission screen and a screenshot of gmail.