variable @fa-css-prefix is undefined on line 4 in file '/Content/icons/fontawesome-5.3.1/less/_rotated-flipped.less':
  [3]: 
  [4]: .@{fa-css-prefix}-rotate-90  { .fa-icon-rotate(90deg, 1);  }
       -^
  [5]: .@{fa-css-prefix}-rotate-180 { .fa-icon-rotate(180deg, 2); }