.box {
  position: relative;
  width: 100%;
  height: 200px;
  text-align: center;
  color: #2828d6;
  background-color: #2828d6;
}
.box:after {
  position: absolute;
  left: 0;
  right: 0;
  bottom: -100px;
  z-index: -1;
  content: ' ';
  height: 100px;
  width: 100%;
  border-radius: 0 0 70% 70%;
  background-color: #2828d6;
}