The ballots are still being counted. The middle grey areas are races that are still too close to call or don't have enough ballots counted to say definitively.

7 gained means so far the democrats have flipped 7 seats previously held by republicans.

It's a little complicated. ALL House seats are up for election every two years. Senate seats are up every six. Governor seats are up to individual state rules.

So some seats are always up for grabs, others not.