FixIt/assets/css/_mixin/_details.scss

@mixin details-transition-open {
  @include transition(max-height 0.2s cubic-bezier(0, 1, 0, 1) -0.1s);
}

@mixin details-transition-close {
  @include transition(max-height 0.2s cubic-bezier(0.5, 0, 1, 0) 0s);
}

details {
  &.center {
    summary {
      text-align: center;
    }
  }
}