A common issue when getting started with the web client is the stream window getting cut off on an iPhone or other device with a smaller screen. This can result in some of the controls or buttons in the game becoming inaccessible to the user.
This is most easily handled by defining the aspect ratio of the streaming element inside the CSS. There's a great walkthrough on w3schools that should cover what you need at https://www.w3schools.com/howto/howto_css_aspect_ratio.asp.
Change the settings to match to whatever your game's default aspect ratio is and you'll have a responsive page that keeps the stream the right size; filling the sides or top and bottom with bars like a letter-boxed movie.
There is a demo site that was created using this strategy at https://sks.pureweb.io/. Try resizing your browser or viewing the demo on a phone or table to see it in action.