Error: ".btn:hover" failed to @extend ".z-depth-half-1".
       The selector ".z-depth-half-1" was not found.
       Use "@extend .z-depth-half-1 !optional" if the extend should be able to fail.
        on line 13 of /home/saper/sw/sass-spec/spec/libsass-todo-issues/issue_1916/input.scss
  Use --trace for backtrace.
