In the rare event this is ever searched for again...
Step one, sit inside car.
Step two, look up at dome light.
Step three, extend arm and reach towards dome light.
Step four, place hand on the clear dome light cover.
Step five, make sure some fingers are on the front edge of the clear dome light cover and some fingers are on the rear edge of the clear dome light cover.
Step six, pinch front and rear edges of dome light cover towards each other.
Step seven, gently pull clear dome light cover away from grey dome light fixture which should stay on the headliner.
Remember if you need to replace your dome light bulb to check what kind of bulb it is. If you are going to buy a replacement in the store bring the old bulb in for comparision. There are two different types of dome light assemblies and thus two different types of dome light bulbs that 6th gen Civics have.