.menu {
background-color: #0000ff;
}
Or, to keep the subtle gradient:
.menu {
background-color: #0000ff;
background-image: -webkit-gradient(linear, left top, left bottom, from(#0000ff), to(#3333ff));
background-image: -webkit-linear-gradient(top, #0000ff, #3333ff);
background-image: -moz-linear-gradient(top, #0000ff, #3333ff);
background-image: -ms-linear-gradient(top, #0000ff, #3333ff);
background-image: -o-linear-gradient(top, #0000ff, #3333ff);
background-image: linear-gradient(top, #0000ff, #3333ff);
filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#0000ff, endColorstr=#3333ff);
}