Question

how does the sea behave at night

Answer 1

Both the Moon and the Sun exert gravitational and centrifugal forces on the Earth's oceans, causing them to bulge out and water to rush up the beaches and create swollen rivers. The Moon's contribution to those forces dominates, despite being so much less massive,  because it is much closer to us than the Sun. 

When all these forces align - when the Earth is in line with the Sun and the Moon, the net force is greater, causing much higher tides. These are called Spring tides. In contrast, when the Earth, Moon, and Sun are perpendicular, you get lower high tides, which are called Neap tides. 

Answer 2

Answer:

The sea gives high tides at night because of both, the Moon and the Sun exert gravitational and centrifugal forces on the Earth's oceans.