Rotates background-image

[bikk1990]

Hi all. I'm a novice here.
It rotates second of two same background-image. Both have same CSS code:

.left-piece {
background-image:url(left-piece.jpg);
background-position:center center;
background-size:cover;
width:300px;
height:300px;
border-radius:300px 300px 0 300px;
}
.right-piece {
background-image:url(right-piece.jpg);
background-position:center center;
background-size:cover;
width:300px;
height:300px;
border-radius:300px 300px 300px 0;
}