When a warm air mass gently slides on top of a cold air mass, and you have drizzly rain and then beautiful sunny weather, what front is it?

It is warm front because it become sunny and warm

A weather front is a boundary separating two masses of air of different densities, and is the principal cause of meteorological phenomena outside the tropics. In surface weather analyses, fronts are depicted using various colored triangles and half-circles, depending on the type of front.