title: rails: any change to custom.css.scss make the app crash
body: <p>I'm learning rails. I have this problem and I hope you can help me.</p>
  
  <p>This is my custome.css.scss:</p>
  
  <pre><code>    @import "bootstrap";
  
  /* mixins, variables, etc. */
  
  $grayMediumLight: #eaeaea;
  
  
  /* universal */
  
  html {
    overflow-y: scroll;
  }
  
  body {
    padding-top: 60px;
  }
  
  section {
    overflow: auto;
  }
  
  textarea {
    resize: vertical;
  }
  
  .center {
    text-align: center;
    h1 {
      margin-bottom: 10px;
    }
  }
  
  /* typography */
  
  h1, h2, h3, h4, h5, h6 {
    line-height: 1;
  }
  
  h1 {
    font-size: 3em;
    letter-spacing: -2px;
    margin-bottom: 30px;
    text-align: center;
  }
  
  h2 {
    font-size: 1.2em;
    letter-spacing: -1px;
    margin-bottom: 30px;
    text-align: center;
    font-weight: normal;
    color: $grayLight;
  }
  
  p {
    font-size: 1.1em;
    line-height: 1.7em;
  }
  
  
  /* header */
  
  #logo {
    float: left;
    margin-right: 10px;
    font-size: 1.7em;
    color: white;
    text-transform: uppercase;
    letter-spacing: -1px;
    padding-top: 9px;
    font-weight: bold;
    line-height: 1;
    &amp;:hover {
      color: white;
      text-decoration: none;
    }
  }
  
  /* footer */
  
  footer {
    margin-top: 45px;
    padding-top: 5px;
    border-top: 1px solid $grayMediumLight;
    color: $grayLight;
    a {
      color: $gray;
      &amp;:hover {
        color: $grayDarker;
      }
    }
    small {
      float: left;
    }
    ul {
      float: right;
      list-style: none;
      li {
        float: left;
        margin-left: 10px;
      }
    }
  }
  </code></pre>
  
  <p>and if I do any change to this file, just like pressing enter (adding an empty line) would make my app crash.</p>
  
  <p>This is the error I get</p>
  
  <pre><code>Undefined variable: "$grayLight".
    (in C:/Sites/rails_projects/sample_app/app/assets/stylesheets/custom.css.scss:52)
  </code></pre>
  
  <p>any help is appreciated. </p>