Use a mixin to style placeholder input text cross browser

placeholder-helper.scss

// use one mixin for styling placeholder input text cross browser
@mixin placeholder ($color) {
  /* WebKit browsers */
  ::-webkit-input-placeholder { 
    color: $color;
  }
  /* Mozilla Firefox 4 to 18 */
  input:-moz-placeholder,
  textarea:-moz-placeholder { 
    color: $color;
  }
  /* Mozilla Firefox 19+ */
  ::-moz-placeholder { 
    color: $color;
  }
  /* Internet Explorer 10+ */
  :-ms-input-placeholder { 
    color: $color;
  }
}