Having trouble with CSS gradients.

[Emily]

I've been developing a XenForo addon and I need a gradient, I made me one but when I put it into the xen_ams.css file it says it's not CSS to use the xentemplate manager to fix the problem? I'm pretty skilled at XenForo but i've never had trouble like this before, here is the gradient if you want to look at it.

background: rgba(73,155,234,1);
background: -moz-linear-gradient(left, rgba(73,155,234,1) 0%, rgba(32,124,229,1) 100%);
background: -webkit-gradient(left top, right top, color-stop(0%, rgba(73,155,234,1)), color-stop(100%, rgba(32,124,229,1)));
background: -webkit-linear-gradient(left, rgba(73,155,234,1) 0%, rgba(32,124,229,1) 100%);
background: -o-linear-gradient(left, rgba(73,155,234,1) 0%, rgba(32,124,229,1) 100%);
background: -ms-linear-gradient(left, rgba(73,155,234,1) 0%, rgba(32,124,229,1) 100%);
background: linear-gradient(to right, rgba(73,155,234,1) 0%, rgba(32,124,229,1) 100%);
filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#499bea', endColorstr='#207ce5', GradientType=1 );