def rounded_corner(horizontal, vertical)
      css = [] << "border"
      attrs = {
        top: "bottom", bottom: "top",
        left: "right", right: "left" }
      css << attrs.fetch(vertical)
      css << attrs.fetch(horizontal)
      css << "radius"
      css.join("-")
    end
def rounded_corner(horizontal, vertical)
      css = [] << "border"
      attrs = {
        top: "bottom", bottom: "top",
        left: "right", right: "left" }
      css << attrs.fetch(vertical)
      css << attrs.fetch(horizontal)
      css << "radius"
      css.join("-")
    end
Returns the CSS needed to round the correct corner

 `border-top-left-radius`