The first light and dark rounds. Video unedited
I crochet a small pattern. You can download the chart and written pattern from this post. You may notice that in the first white round on the short sides I crochet 2 sc and 1 dc. It matches this pattern. Instead, you can crochet 3 sc.
Solid corners, which are called L-corner in the Midsummer Night's Dream pattern, are best crocheted as I show in the video https://www.patreon.com/posts/overlay-mosaic-70472591
In this way, you can start crocheting in the round for any rectangular mosaic pattern.
I hope this video is helpful. Ask questions, please. I'll try to give an explanation.