>>The other big option is to use responsive design (CSS) to rearrange the layout of your page. You show and hide things based on the resolution of the screen. Some frameworks like Bootstrap can also help with automatically reflowing horizontal content vertically (ie. two column layouts become to stacked rows) etc.
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>There must be more info deciding layout - LG G3/G4 have the same resolution as my (not totally current) 27' and in 10' tablets you can have density of just sub-HD. Sometimes I am not very sorry I am more of a bizlayer/backend dev ;-)

That's what the ViewPort tag is for :-)

It limits the device to a specified fixed pixel/inch size. For example an iPhone 4s was 320x480, which is pretty standard for 4" phones at the time. I think now the widths are creeping up but not massively. My iPhone 6 (standard) renders at ~360px width.

+++ Rick ---