Modify text-shadow and letter-spacing of menu items

Summary

Modify the text-shadow and letter-spacing attributes in menu items. The values should be the following:

header .nav > li > a{
   text-shadow: 0px 0px 0.8px black, 0px 0px 0.8px white, 0px 0px 0.8px black, 0px 0px 0.8px white, 0 0 0.8px white; 
   letter-spacing: 0.5px; 
}