body {
  padding-top: 15ex;
  header.header {
    width: 100%;
    position: fixed;
    top: 0;
    padding: 0 5%;
    background-color: $cloud;
    color: $sky;
    z-index: 999;
    h1 {
      width: 10em;
      float: left;
    }
    nav {
      float: right;
      ul {
          vertical-align: text-bottom;
        li {
          list-style: none;
          display: inline-block;
          padding:3ex 1em;
        }//li
      }//ul
    }//nav
  }//.header
}//body

body {
  padding-top: 15ex;
  header.header {
    width: 100%;
    position: fixed;
    top: 0;
    padding: 0 5%;
    background-color: $sky;
    color: $cloud;
    z-index: 99;
    a[href] {
      color: $cloud;
      text-decoration: none;
      &:hover {
        color: darken($cloud, 10%);
      }
    }
    h1 {
      width: 10em;
      float: left;
      font-size: 7em;
      line-height: 0;
      margin-bottom: 0;
    }
    nav {
      float: right;
      ul {
          vertical-align: text-bottom;
        li {
          list-style: none;
          display: block;
          float: right;
          font-size: 1.5em;
          padding: 1.5ex 1em;
        }//li
      }//ul
    }//nav
  }//.header
}//body

Change background color to sky, zindex to 99 and color to cloud.
Change background color to sky, zindex to 99 and color to cloud.
