.sibianaojiao {
height: 100px;
margin: 40px;

background: #58a;
background: radial-gradient(circle at top left,
transparent 15px, #58a 0) top left,
radial-gradient(circle at top right,
transparent 15px, #58a 0) top right,
radial-gradient(circle at bottom right,
transparent 15px, #58a 0) bottom right,
radial-gradient(circle at bottom left,
transparent 15px, #58a 0) bottom left;
background-size: 50% 50%;
background-repeat: no-repeat;
border-radius: 15px;

/*  corner-shape: bevel; */

}

凹面
.box {
position: relative;
overflow: hidden;
&::before {
content: '';
position: absolute;
padding: 20px;
left: 80px;
/* right: 35px; /
/ top: 26px; /
bottom: 443px;
/ -webkit-box-shadow: 0 0 7px #b53; /
/ box-shadow: 0 0 7px #b53; */
background: #95a;
border-radius: 50%;
box-shadow: 0 0 0 300px #3a8ee6;
}
}