Curved background

<div class="curved-background">
    <div class="curved-background__curved"></div>
</div>

.curved-background__curved {
    /* Background color */
    background-color: #d1d5db;

    /* You can use gradient background color such as */
    /* background: linear-gradient(rgba(0, 0, 0, 0.2) 0%, rgba(0, 0, 0, 0.1) 100%); */

    /* Curved corners */
    border-bottom-left-radius: 50% 40%;
    border-bottom-right-radius: 50% 40%;

    /* Size */
    height: 50%;
    width: 100%;
}