以下のCSSを仕込めばOK
.pretty.navbar {
background-image: linear-gradient(#FFFFFF, #FFFFFF);
-webkit-box-shadow: inset 0 1px 1px #FFFFFF, 0 1px 2px rgba(255, 255, 255, 0.8) !important;
-moz-box-shadow: inset 0 1px 1px #7b8085, 0 1px 2px rgba(0, 0, 0, 0.8) !important;
box-shadow: inset 0 1px 1px #FFFFFF, 0 1px 2px rgba(255, 255, 255, 0.8) !important;
}
↓