Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.4)
// Compass (v1.0.0.alpha.18)
// ----

@mixin calc-width($percentage, $width) {
  /* Firefox */
  width: -moz-calc(#{$percentage} - #{$width});
  /* WebKit */
  width: -webkit-calc(#{$percentage} - #{$width});
  /* Opera */
  width: -o-calc(#{$percentage} - #{$width});
  /* Standard */
  width: calc(#{$percentage} - #{$width});
}

@mixin calc-height($element, $percentage, $pixels) {
  /* Firefox */
  $element: -moz-calc(#{$percentage} - #{$pixels});
  /* WebKit */
  $element: -webkit-calc(#{$percentage} - #{$pixels});
  /* Opera */
  $element: -o-calc(#{$percentage} - #{$pixels});
  /* Standard */
  $element: calc(#{$percentage} - #{$pixels});
}
.white-triangle {
  width: 0;   height: 0;   
  border-top: 30px solid transparent;  
  border-bottom: 30px solid transparent;
  border-right: 20px solid white;
  position: absolute;
  @include calc-height("top", "50%", "15px");
  @include calc-width("50%", "15px");
  right: 0;
  // top: 50%;
}

SassMeister-output.css

.white-triangle {
  width: 0;
  height: 0;
  border-top: 30px solid transparent;
  border-bottom: 30px solid transparent;
  border-right: 20px solid white;
  position: absolute;
  /* Firefox */
  /* WebKit */
  /* Opera */
  /* Standard */
  /* Firefox */
  width: -moz-calc(50% - 15px);
  /* WebKit */
  width: -webkit-calc(50% - 15px);
  /* Opera */
  width: -o-calc(50% - 15px);
  /* Standard */
  width: calc(50% - 15px);
  right: 0;
}