«أَقَلَّهُمَا غُصْنٌ»
A branch supported them both.
Aqalla here means to lift or support, while ghuṣn means a branch. The slender, graceful branch metaphorically denotes the woman's body, bearing the dark hair and bright face in the picture.
The metaphor ties the parts together: night is hair, morning is face, and branch is the body. The poem does more than praise beauty; it constructs a coherent scene from natural images.