There are issues with the scaling of certain UI elements in high dpi environments.
On the 4K display of my desktop, this is mostly an aesthetic problem:
- the buttons on pop-up windows (such as the clean up dialog) are oversized and sometimes overlay each other (this was already reported here http://forum.shuffleit.nl/index.php?topic=1338.0
- the radio buttons on the autoplay options are oversized and pixelated
However, when trying to use the game on a small, very high dpi display, the scaling issues make it almost impossible to use. I played one game on a Samsung Galaxy S7 using Chrome. Obviously, playing on such a small screen will always have drawbacks (unless you have really sharp eyes and use a stylus), amd supporting play on a phone outside of a dedicated app may not be a target for you. But still, that is not an excuse for zooming working in such an inconsistent way:
- Many UI elements (cards in the supply, log, VP counter, button labels...) keep a constant pixel size, so shrink with the higher dpi.
- Other UI elements (cards you play, button borders) keep a constant absolute size, so grow enormous. This is especially jarring on buttons, which grow huge with minuscule text
- certain areas (log) are fixed w.r.t. the view port. So you cannot just zoom and pan, but a certain part of the screen is always taken up with these elements. On the after game results page, both the log and game options are fixed, and the font in the actual game results column in the middle is so large that the scores are cut off, with no way of zooming, panning, or otherwise making them visible.
I don't expect the game to be playable on a phone, but I would fix this from an engineering point of view. Who knows how soon 8K displays become available...