In general, discussions here along those lines are not very productive - if events follow their historical outcome up to the Fall of France, there is no way that Sealion can be successful.
If you mean, what if it's launched anyway, then a not completely unviable answer is that:
British:
The RAF takes additional losses, up to 200% above the historical loss rates.
The RN loses 1 battleship, half a dozen cruisers, 20 destroyers, and a large number of armed trawlers and fast attack craft.
The Army takes an additional 12,000 casualties.
German
35,000 troops are casualties or prisoners.
Most of the available Kriegsmarine is sunk.
The Luftwaffe takes such losses (including among the transport arm which was just reconstituting after losses in April) that its ability to support a Barbarossa is in question
The losses among the invasion barges are a significant blow to the internal German economy as they are not available to transport goods over the internal river network.
British casualties are not from elements historically associated with the North African campaign, but the Luftwaffe losses may draw replacements from elements historically used in the Med.
However, the need to resupply the home defence formations is likely to mean that the British Operation Compass is not better supplied and/or more successful.
The Greek campaign is likely to have a less aggressive Greek strategy, as Churchill has more room to argue that recovery from the invasion makes Britain less able to support Greece, which in turn will make the Greek defence more successful, though ultimately German intervention will be decisive.
The transport losses will prevent the historical air assault on Crete and it will be held as a Free Greek stronghold.
If Hitler pushes ahead with Barbarossa, then the historical ability of Luftwaffe close air support to break Soviet strongpoints is compromised and the rate of advance is likely to be slower... but that's too complex a set of circumstances to casually scribble about before I have to take my son to school.