Two techniques: overlay mosaic and interlocking filet crochet. Rectangular or square, worked either in the round from the center or bottom-up. Either just the main panel with envelope border in the round (for interlocking crochet – border in the round), or the full width as you go.

There is also a version with the moon and flowers highlighted in an additional color.
⚠️ Multiple colors version – bottom-up only.

Size:
Rectangular (full width): 301 st × 391 rows

Sport yarn: approx. 140 × 180 cm (55 × 70”), hook 3.25-3.5, gauge 11 st × 11 rows in 5 cm (2”) in dc pattern
Fingering yarn: approx. 105 × 135 cm (41 × 53”), hook 2.5, gauge 29 st × 29 rows in 10 cm (4”) in dc pattern

Square: 301 st × 301 rows

Sport yarn: approx. 140 × 140 cm (55 × 55”), hook 3.25-3.5, gauge 11 st × 11 rows in 5 cm (2”) in dc pattern
Fingering yarn: approx. 105 × 105 cm (41 × 41”), hook 2.5, gauge 29 st × 29 rows in 10 cm (4”) in dc pattern

Approximate yarn requirements (not including the reverse side of the envelope border):

Rectangular blanket
Sport weight:
Light: ~3910 m / 4277 yds
Dark: ~4000 m / 4376 yds

Fingering weight:
Light: ~2520 m / 2757 yds
Dark: ~2580 m / 2823 yds

Square blanket
Sport weight:
Light: ~3030 m / 3315 yds
Dark: ~3080 m / 3370 yds

Fingering weight:
Light: ~1950 m / 2133 yds
Dark: ~1990 m / 2177 yds