how to make curved div in css code example

Example 1: css rounded corners

/* Set rounded corners with border-radius property */

.class {
  border-radius: 4px;
}

.circle {
  border-radius: 50%;
}

Example 2: css rounded corners

/* Use border-radius property */

.class {
  border-radius: 5px;
}

.circle {
  border-radius: 50%;
}

Example 3: curve bottom of square css

.round-bottom { 
  border-bottom-left-radius: 50% 150px !important;
  border-bottom-right-radius: 50% 150px !important;
  position: relative;
  overflow: hidden;
  width: 160%; 
  margin-bottom:-50px;
  left:-30%; 
  background-color:#444;
  background-image: url('https://upload.wikimedia.org/wikipedia/commons/a/a2/Tropical_Forest_with_Monkeys_A10893.jpg'); background-position: center center;
  background-size: 42% auto;
  height:150px;
}
.container { width: 100%; height: height:100px; padding-bottom:50px; overflow:hidden;}

<div class="container"><div class="round-bottom"></div></div>