Curved background
HTML
<div class="curved-background">
<div class="curved-background__curved"></div>
</div>
CSS
.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%;
}
Demo