Media Queries

The nesting Sass feature keeps media queries local to the original selector being modified. You can avoid repeating the values in media query expressions with variables.

CSS

.img-featured {
  width: 165px;
  border: 4px solid white; 
  border-radius: 50%;
  margin-top: 75px;
  position: relative;
  z-index: 100;
}
@media (max-width: 575px) {
  .img-featured {
  	display: none;
  }
}

Written in Sass like so:
SCSS

.img-featured {
    width: 165px;
    border: 4px solid white; 
    border-radius: 50%;
    margin-top: 75px;
    position: relative;
    z-index: 100;

    @media (max-width: $break-xs) {
        display: none;
    }
}

Whereas the _variables.scss partial has the following variables:

// Breakpoints
$break-xs: 575px;
$break-s: 576px;
$break-m: 768px;
$break-l: 992px;
//...