The release of our skins for Roundcube 9.x brought about the best and the latest that technology has to offer. One of the major improvements was including SVG images in all the mobile skins.
And what's so great about SVG? It solves icon display problems on the modern high-resolution smartphones. Because the smartphone screens nowadays use more and smaller pixels, they scale up whatever they display to make it readable to human eyes. When fonts are scaled it's not a problem because they are vector-based and when their size changes they don't lose quality. But images like JPEG or PNG are not vector-based and when they scale up, they become blurred.
The cutting-edge solution is to use vector-based SVG images that scale without losing quality. This is what we did with all our mobile skins.
The problem is that the older smartphones don't support the display of SVG images, so on some phones the Roundcube icons wouldn't display at all. We have now upgraded our mobile skins to include a fallback mechanism to PNG icons if the browser doesn't support SVG.
If you're using our mobile skins, we recommend that you re-download their latest versions from our customer area to make sure that the icons display properly for all your webmail users.