Chained until long enough,
hdc into second ch from hook, hdc in every ch, ch1, turn, hdc in first stitch - but under loop directly below front loop (back of the previous row’s hdc) to creat ribbing effect. Repeat every row.

https://yarnandchai.com/tutorial-ribbed-half-double-croch...

I think the variegated yarn looks a bit too busy in the photos but it looks great in person!