Например, так:
background: #2e5a89; /* Old browsers */
background: -moz-radial-gradient(center, ellipse cover, #2e5a89 0%, #16283e 100%); /* FF3.6+ */
background: -webkit-gradient(radial, center center, 0px, center center, 100%, color-stop(0%,#2e5a89), color-stop(100%,#16283e)); /* Chrome,Safari4+ */
background: -webkit-radial-gradient(center, ellipse cover, #2e5a89 0%,#16283e 100%); /* Chrome10+,Safari5.1+ */
background: -o-radial-gradient(center, ellipse cover, #2e5a89 0%,#16283e 100%); /* Opera 12+ */
background: -ms-radial-gradient(center, ellipse cover, #2e5a89 0%,#16283e 100%); /* IE10+ */
background: radial-gradient(ellipse at center, #2e5a89 0%,#16283e 100%); /* W3C */
filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#2e5a89', endColorstr='#16283e',GradientType=1 ); /* IE6-9 fallback on horizontal gradient */