Generated by SassMeister.com.

SassMeister-input.scss

// ----
// libsass (v3.0.1)
// ----

@mixin displayTransition($selector, $time, $hidden: '', $visible: '') {
  
  $hidden: if($hidden != '', ', ' + $hidden, $hidden);
  $visible: if($visible != '', ', ' + $visible, $visible);
  
  visibility: hidden;
  opacity: 0;
  transition: visibility 0s linear $time, opacity $time linear#{$hidden};

  #{$selector} {
    visibility: visible;
    opacity: 1;
    transition: visibility 0s linear 0s, opacity $time linear#{$visible};
  }
}

.block {
  @include displayTransition('&.block--visible', 0.35s, 'height .35s ease-out');
}

SassMeister-output.css

.block {
  visibility: hidden;
  opacity: 0;
  transition: visibility 0s linear 0.35s, opacity 0.35s linear, height .35s ease-out; }
  .block.block--visible {
    visibility: visible;
    opacity: 1;
    transition: visibility 0s linear 0s, opacity 0.35s linear; }