These two verses complete the set of the literary parallels introduced by the "day of the Lord." The theme continues to be destruction. with these verses concentrating on the destruction of the wicked.
Literary: While the darkness of the world in verse 10 may have a physical counterpart t the end of the world, it is also a literary device that presages the message of verse 11. Verse 10 contrasts the darkness with current light. In this case, it is not the bad/good contrast symbolized by the darkness and light, but rather the alteration of the natural order. Those entities that ought to give light are dark. This is a poetic reversal that underscores the just-as-unusual reversal where the wicked do not reign, but are brought down, and the mighty humbled.