SOURCE

<div></div>

body{background: #ff0000}

div{
    position: relative;
    width:600px;
    height: 300px;
    border-radius: 6px;
    background: 
    radial-gradient(circle at 0% 0%, transparent 8%, #fff 8.3%,#fff 20%,transparent 22%) no-repeat left / 50% 100%,
    radial-gradient(circle at 100% 0%, transparent 8%, #fff 8.3%,#fff 20%,transparent 22%) no-repeat right / 50% 100%,
    radial-gradient(circle at 0% 100%, transparent 8%, #fff 8.3%,#fff 20%,transparent 22%) no-repeat left / 50% 100%,
    radial-gradient(circle at 100% 100%, transparent 8%, #fff 8.3%,#fff 20%,transparent 22%) no-repeat right / 50% 100%
}
/* div::before {
    content:"";
    width: 80%;
    height: 1px;
    border-top: 2px dotted #ccc;
    position: absolute;
    left: 10%;
    top: 35%;
    pointer-events: none;
} */