css 實現弧形背景

.pure_top {
 width: 100%;
 height: 100px;
 position: relative;
 z-index: 0;
 overflow: hidden;
}
.pure_top::after {




 content: '';
 width: 120%;
 height: 100px;
 position: absolute;
 left: -10%; //橢圓左邊隱藏10%，右邊隱藏10%




 top: 0;
 border-radius: 0 0 50% 50%; //左上角，右上角，右下角，左下角
 background: #1496f1;
}