Some simple CSS to define a background gradient.

gradient.css

header nav {
  position: relative;
  border-top: 1px solid #73BBCF;
  border-bottom: 1px solid #73BBCF;
}

header nav {
  padding: 12px 0;
  font-weight: bold;
  font-size: 0.875em;
  background-image: -moz-linear-gradient(top, #008DC2 0%, white 25%);
  background-image: -webkit-linear-gradient(top, #008DC2 0%, white 25%);
  background-image: -ms-linear-gradient(top, #008DC2 0%, white 25%);
  background-image: -o-linear-gradient(top, #008DC2 0%, white 25%);
  background-image: linear-gradient(top, #008DC2 0%, white 25%);
}