Add support for responsive

[roguexiaohuihui]

Currently height and width are written in pixels，This can lead to fatal experience problems if you use different browser resolutions。

This requirement is very important. I wonder if you have any good solutions to discuss or improve with us

[lucasvazq]

bump

[gdevdeiv]

You can also use percentage-based values, like 100%.

But it would be interesting to be able to play with the display property and flex. Note that this could require some kind of hierarchy... but this should be treated in another issue.