nav:
  -
    slug: "grid-system"
    title: "Grid System"
    nav:
      -
        slug: "grid-introduction"
        title: "Introduction"
      -
        slug: "grid-simple"
        title: "Ex: Simple"
      -
        slug: "grid-nested"
        title: "Ex: Nested"
      -
        slug: "grid-spaced"
        title: "Ex: Spaced"
      -
        slug: "grid-center"
        title: "Ex: Center"
  -
    slug: "responsive-design"
    title: "Responsive Design"
    nav:
      -
        slug: "responsive-introduction"
        title: "Introduction"
      -
        slug: "responsive-helpers"
        title: "Helpers"
      -
        slug: "responsive-examples"
        title: "Ex: desktop & mobile"