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>