trusted-setup-server/assets/styles/components/_fieldset.scss

fieldset {
  &:not(:last-child) {
    margin-bottom: $block-spacing;
  }

  &.authorize {
    max-width: 30%;
    margin-left: auto;
    margin-right: auto;
  }

  &[disabled] {
    opacity: .5;
    cursor: not-allowed;

    label {
      cursor: inherit;
    }
  }
}