Looking sleek as per, I'd would look to use these black caps if they'd fit the recess.
https://m.ebay.co.uk/itm/128-NUMBER-PLATE-CAR-FIXING-FITTING-KIT-HINGE-CAPS-SCREWS-YELLOW-BLACK-WHITE-REG/350359071434?epid=1555729101&hash=item5193072aca:g:AlUAAOSwiYFXI0IY