Fiddle
.box {
position: relative;
width: 95%;
margin: 50px auto;
}
.box > img, .box > div {
max-width: 100%;
}
.vignette {
position: absolute;
top: 0;
left: 0;
bottom: 0;
right: 0;
z-index: 1;
background: -moz-radial-gradient(center, ellipse cover, rgba(255, 255, 255, 0) 0%, rgba(255, 255, 255, 0) 33%, rgba(255, 255, 255, 1) 100%);
/* FF3.6+ */
background: -webkit-gradient(radial, center center, 0px, center center, 100%, color-stop(0%, rgba(255, 255, 255, 0)), color-stop(33%, rgba(255, 255, 255, 0)), color-stop(100%, rgba(255, 255, 255, 1)));
/* Chrome,Safari4+ */
background: -webkit-radial-gradient(center, ellipse cover, rgba(255, 255, 255, 0) 0%, rgba(255, 255, 255, 0) 33%, rgba(255, 255, 255, 1) 100%);
/* Chrome10+,Safari5.1+ */
background: -o-radial-gradient(center, ellipse cover, rgba(255, 255, 255, 0) 0%, rgba(255, 255, 255, 0) 33%, rgba(255, 255, 255, 1) 100%);
/* Opera 12+ */
background: -ms-radial-gradient(center, ellipse cover, rgba(255, 255, 255, 0) 0%, rgba(255, 255, 255, 0) 33%, rgba(255, 255, 255, 1) 100%);
/* IE10+ */
background: radial-gradient(ellipse at center, rgba(255, 255, 255, 0) 0%, rgba(255, 255, 255, 0) 33%, rgba(255, 255, 255, 1) 100%);
/* W3C */
}