How do I calculate a PCB embedded capacitor? (2 in series)
The package is 15mm by 10mm. Your overlap, on each side, looks to be 10mm by 20mm. The 8mil spacing, in 4layer PCB, is 1/5th mm.

Capacitance is E0*Er*Area/Distance = 9e-12Farad/meter * FR4=4 * 200mm^2/(1/5mm)

C (one cap) is 36e-12 * 200/0.2 * 1meter/1000mm
C = 36e-12 * 1000 / 1000 = 36 picoFarad.

Two in series is 18pF.

How accurate is this? aspect ratio is 10mm by 1/5mm or 50:1. The capacitor has less than 10% error.