<div id="box" class="okragle-dwa-rogi"> </div>

#box {
	width: 100px;
	height: 100px;
	background: red;
}

.okragle-dwa-rogi {
	-webkit-border-top-right-radius: 20px; /* prawy górny */
	-webkit-border-bottom-left-radius: 20px; /* lewy dolny */
	-khtml-border-radius-topright: 20px;
	-khtml-border-radius-bottomleft: 20px;
	-moz-border-radius-topright: 20px;
	-moz-border-radius-bottomleft: 20px;
	border-top-right-radius: 20px;
	border-bottom-left-radius: 20px;
}