Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.13)
// Compass (v1.0.3)
// ----

.js {
  .slider-grid {
    .content-tile {
      border: 1px solid red;
      
      @at-root #{selector-append(".ie9", &)} {
        color: red;
      }
    }
  } 
} 

SassMeister-output.css

.js .slider-grid .content-tile {
  border: 1px solid red;
}
.ie9.js .slider-grid .content-tile {
  color: red;
}