.box

body {
   background: url(https://picsum.photos/id/237/1000?blur) no-repeat center center / cover;
   display: flex;
   align-items: center;
   justify-content: center;
   height: 100vh;
}

.box {
   width: 300px;
   height: 200px;
   box-shadow: 0 0 0 20px rgba(255, 255, 255, 0.2);
   background-color: #619EA1;
}