bunu farklı yerlere de uyarlayabilirsin. yapamazsan pm at yardımcı olayım.

.td-header-menu-wrap-full {
background: red;
background: -webkit-linear-gradient(left,red,orange,yellow,green,blue,indigo,violet);
background: -o-linear-gradient(left,red,orange,yellow,green,blue,indigo,violet);
background: -moz-linear-gradient(left,red,orange,yellow,green,blue,indigo,violet);
background: linear-gradient(to right, red,orange,yellow,green,blue,indigo,violet);
}