WHOLE CHARACTER
复
to return; to recover; to reply; again; once more; to repeat; to review; complicated
复 stacks a small mark over 日 and the bent 夂 piece: review lessons (复习), repeat things (重复), and recover (恢复).
ZDIC: 形声 — the historical 復 joined a movement piece with a reduced sound side. The modern simplified shape writes a small top mark over 日 and the bent 夂 piece; shown as a visual aid, the middle box is not the word 'sun' here.