How to set responsive CSS design size?

Question

css

The object
needs to be set to adaptability, that is, to specify width 100px height 100px in one place so that the entire structure changes its size proportionally, as it is now, so that nothing flies anywhere.
How to implement?
and link to this thread please.
UPD: was applied transform:scale(0.5);
But the essence of the question was how to make adaptive content?
That is, if you make the parent 200px and all children in% specify width and heught, can you achieve a good adaptive with this method?