title: Sass lighten function issue
body: <p>Well, I have a problem with Sass function <code>lighten()</code>, this is my code:</p>
  
  <pre><code>@for $i from 1 through 4{
      .par-#{$i}{
          background: lighten(#08725D, #{$i}0%);
          padding: 10px;
          border-radius: 5px;
      }
  }
  </code></pre>
  
  <p>I think it's pretty obvious what I want to do, I just want to go through that variable and increment the lightening of the bg color (while I increment the number in the class), but I have this error in console: </p>
  
  <blockquote>
    <p>error main.scss (Line 111: $amount: "10%" is not a number for `lighten')</p>
  </blockquote>
  
  <p>I need help please.</p>