.box-shadow is undefined in Laravel5.2

[boybeak]

I download the resources and put the folders under resources/assets, then edit the gulpfile.js file as below:

elixir(function(mix) {
    mix.less('bootstrap-markdown.less');
    mix.styles('bootstrap-markdown.min.css');
    mix.scripts('bootstrap-markdown.js');
    mix.sass('app.scss');
});

After this, run gulp, and comes out error msg:

gulp-notify: [Laravel Elixir] Less Compilation Failed: .box-shadow is undefined in file /usr/local/var/www/nulldreams/resources/assets/less/bootstrap-markdown.less line no. 66
{ [Error: .box-shadow is undefined in file /usr/local/var/www/nulldreams/resources/assets/less/bootstrap-markdown.less line no. 66]
  type: 'Name',
  filename: '/usr/local/var/www/nulldreams/resources/assets/less/bootstrap-markdown.less',
  index: 1451,
  line: 66,
  callLine: NaN,
  callExtract: undefined,
  column: 4,
  extract: 
   [ '    outline: 0;',
     '    .box-shadow(~"inset 0 1px 1px rgba(0,0,0,.075), 0 0 8px @{color-rgba}");',
     '  }' ],
  message: '.box-shadow is undefined in file /usr/local/var/www/nulldreams/resources/assets/less/bootstrap-markdown.less line no. 66',
  stack: undefined,
  lineNumber: 66,
  fileName: '/usr/local/var/www/nulldreams/resources/assets/less/bootstrap-markdown.less',
  name: 'Error',
  showStack: false,
  showProperties: true,
  plugin: 'gulp-less',
  __safety: { toString: [Function] } }

Why .box-shadow is undefined.

[pscheit]

the mixin for scss is missing as well