/*
Error: Undefined mixin 'min-screen'.
        on line 2 of animation.scss, in `min-screen'
        from line 2 of animation.scss

1: 
2: @include min-screen(992px){
3:   @keyframes letter-space{
4:     0% {letter-spacing: 5px;}
5:     50% {letter-spacing: 15px;}
6:     100% {letter-spacing: 5px;}
7:   }

Backtrace:
animation.scss:2:in `min-screen'
animation.scss:2
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/perform.rb:348:in `block in visit_mixin'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/stack.rb:98:in `block in with_mixin'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/stack.rb:135:in `with_frame'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/stack.rb:98:in `with_mixin'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/perform.rb:346:in `visit_mixin'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/base.rb:36:in `visit'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/perform.rb:158:in `block in visit'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/stack.rb:79:in `block in with_base'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/stack.rb:135:in `with_frame'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/stack.rb:79:in `with_base'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/perform.rb:158:in `visit'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/base.rb:52:in `block in visit_children'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/base.rb:52:in `map'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/base.rb:52:in `visit_children'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/perform.rb:167:in `block in visit_children'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/perform.rb:179:in `with_environment'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/perform.rb:166:in `visit_children'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/base.rb:36:in `block in visit'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/perform.rb:186:in `visit_root'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/base.rb:36:in `visit'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/perform.rb:157:in `visit'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/visitors/perform.rb:10:in `visit'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/root_node.rb:36:in `css_tree'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/tree/root_node.rb:29:in `render_with_sourcemap'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/engine.rb:389:in `_render_with_sourcemap'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/engine.rb:307:in `render_with_sourcemap'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/plugin/compiler.rb:462:in `update_stylesheet'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/plugin/compiler.rb:215:in `block in update_stylesheets'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/plugin/compiler.rb:209:in `each'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/plugin/compiler.rb:209:in `update_stylesheets'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/plugin.rb:82:in `update_stylesheets'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/exec/sass_scss.rb:338:in `watch_or_update'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/exec/sass_scss.rb:51:in `process_result'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/exec/base.rb:50:in `parse'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/lib/sass/exec/base.rb:18:in `parse!'
C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/sass-3.7.2/bin/scss:13:in `<top (required)>'
C:/Ruby25-x64/bin/scss:23:in `load'
C:/Ruby25-x64/bin/scss:23:in `<main>'
*/
body:before {
  white-space: pre;
  font-family: monospace;
  content: "Error: Undefined mixin 'min-screen'.\A         on line 2 of animation.scss, in `min-screen'\A         from line 2 of animation.scss\A \A 1: \A 2: @include min-screen(992px){\A 3:   @keyframes letter-space{\A 4:     0% {letter-spacing: 5px;}\A 5:     50% {letter-spacing: 15px;}\A 6:     100% {letter-spacing: 5px;}\A 7:   }"; }