Hi,
First of all, as you said it may be a css issue.
But, from my understanding, it’s the issue with the scale. If it is in desktop, suppose the scale is 1, and window size is 1024, then icons will be visible as expected.
But, if the same scale is using for devices with lower screen width, may cause the icon size very much. And, it will reduce the icon size and icons may disappear.
Please share your webpage address for further details. The analysis of the issue is free of cost.
Thanks,
Jithil