Keep the lids in place and buy extenders to sit around them that
extend past ground level. The extenders have lids on them that may
have to be purchased separately. The lids underground (the ones you
already have) will remain in place

The 12" extensions sit flush in/on the existing tank opening and the normal
"cap" fits them fine..no need for two "lids".
I used two for my tank. They told me there were 8" (and 24's) extensions
also available.
If you just want to go with what's there already, cover the "naked" caps
with a piece of sheet plastic and throw some wood chips/mulch over top for
decor purposes. I incorporated this method into a rock mulch covered
landscape feature, effectively 'hiding' the caps.