boder raious round css code example

Example 1: css circle border

.circle {
    background-color:#fff;
    border:1px solid red;    
    height:100px;
    border-radius:50%;
    -moz-border-radius:50%;
    -webkit-border-radius:50%;
    width:100px;
}
<div class="circle"></div>

Example 2: 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>