Generated by SassMeister.com.

SassMeister-input-HTML.html

<table class="mytable">
  <tfoot>
    <tr>
      <td class="mytd">
        Hello
      </td>
    </tr>
  </tfoot>
</table>

SassMeister-input.scss

// ----
// Sass (v3.4.6)
// Compass (v1.0.1)
// ----

%acx-table {
  > tfoot {
    > tr {
      > %acx-th,
      > %acx-td {
        color: red;
      }
    }
  }
}

table {
  @extend %acx-table;  
}

td {
  @extend %acx-td;
}

.mytable {
  @extend %acx-table;
}

.mytable .mytd {
  color: blue;
}

SassMeister-output.css

table > tfoot > tr > td,
.mytable > tfoot > tr > td {
  color: red;
}

.mytable .mytd {
  color: blue;
}

SassMeister-rendered.html

<table class="mytable">
  <tfoot>
    <tr>
      <td class="mytd">
        Hello
      </td>
    </tr>
  </tfoot>
</table>