title: sass : get child's property from inside parent styling
body: <p>i have a group of cards with specific class for each ,
  they all have a uniting general class</p>
  <p>each specific card needs a border that is slightly darker than its background-color</p>
  <p>so is there a way to make the general class styling apply a border that is based on the current background-color using sass</p>
  <pre><code>.general{
    display:flex; /*bla bla bla*/
    border:10px solid darken( *insert specific color here* , 10% );
  }
  .general.specific-1{
    background-color:red;
  }
  .general.specific-2{
    background-color:blue;
  }
  .general.specific-3{
    background-color:crimson;
  }
  
  </code></pre>