In what direction is the relief of the East European Plain going down?

A relief decrease occurs in the East European Plain in the northern part and moves towards the White and Barents Seas. This part of the plain is called the Northern Slope. In the north of the plain, the following rivers flow: Pechora, Northern Dvina, Onega, Mezen.
The lowlands of the East European Plain occupy the southern part. Caspian Sea is located in Russian Federation. Rivers such as the Volga, Don, Volga tributaries flow to the south of the plain and flow into the Caspian, Azov and Black seas. To the south is the slope of the southern part of the East European Plain.