title: ::-webkit-input-placeholder does not work
body: <p>i'm writing a mobile web sites and i'm styling it with sass.</p>
  
  <p>I would like to change the placeholder color of textinput, but i'm not able to do this.</p>
  
  <p>This is the mixin for the placeholder</p>
  
  <pre><code>@mixin placeholder($color) {
    ::-webkit-input-placeholder {color: $color}
    :-moz-placeholder           {color: $color}
    ::-moz-placeholder          {color: $color}
    :-ms-input-placeholder      {color: $color}
  }
  </code></pre>
  
  <p>And then i use it included into a class</p>
  
  <pre><code>.input-class {
      @include placeholder(#FFFFFF);
  }
  </code></pre>
  
  <p>Finally set the class to the input</p>
  
  <pre><code>&lt;input class="input-class" ...&gt;
  </code></pre>
  
  <p>But nothing happens. In addition my IDE set an error on the mixins lines saying me: "Unknown pseudo selector -webkit-input-placeholder" and chrome seems to not recognize that tag.</p>
  
  <p>How can I change the color of placeholder? No matter if the response is in sass or css.</p>
  
  <p>Thanks in advance.</p>