No CSS class defined

Dear Sir/Madam,

When viewing the invoice page, there is a footer

<div class="pswp__top-bar">
				<div class="pswp__counter"></div>
				<button class="pswp__button pswp__button--close" aria-label="Close (Esc)"></button>
				<button class="pswp__button pswp__button--share" aria-label="Share"></button>
				<button class="pswp__button pswp__button--fs" aria-label="Toggle fullscreen"></button>
				<button class="pswp__button pswp__button--zoom" aria-label="Zoom in/out"></button>
				<div class="pswp__preloader">
					<div class="pswp__preloader__icn">
						<div class="pswp__preloader__cut">
							<div class="pswp__preloader__donut"></div>
						</div>
					</div>
				</div>
			</div>

The buttons are associated with the wpi-unified-page.css but I don’t find the style for element pswp__button pswp__button–close, pswp__button pswp__button–share, etc.

Is there any bug?

Best regards,

Kelvin.