.sr-only {
  @extend .visually-hidden;
}
// embed responsive 
.embed-responsive {
  @extend .ratio;
}
.embed-responsive-21by9 {
  @extend .ratio-21x9;
}
.embed-responsive-16by9 {
  @extend .ratio-16x9;
}
.embed-responsive-4by3 {
  @extend .ratio-4x3;
}
.embed-responsive-1by1 {
  @extend .ratio-1x1;
}