Here's why:

* Clouds are made of water droplets or ice crystals. These droplets/crystals scatter and reflect sunlight in all directions.

* The sunlight that is scattered and reflected upward can't reach the ground. This is why it's often darker under the clouds.

* The sunlight that passes through the gaps between clouds can reach the ground, creating sunny patches.

* Above the clouds, there is no longer anything to block the sunlight. It shines directly on the surface of the clouds, making it appear bright and sunny.

Think of it like this: imagine you're standing in a dense forest. The trees block the sunlight from reaching the ground, but if you climb a tall tree, you'll be above the canopy and bathed in sunlight. The clouds are like the canopy, blocking sunlight from reaching the ground, but above them, you're in the clear.