On the top and on the left of the page there are rulers (I don't know if this is the exact name, but see attached image) which allow you to resize the selected item.
They always have pixel size indication, even if the selected item size is relative to another object (for example % of the table, % of the window, ...).
If you resize an element dragging the ruler, its size is forced to "pixels" even if it was in "% of".
I would suggest this nice behaviour: if the size of the selected item is in "% of", this unit should be shown into the ruler; when you resize this element dragging the ruler, the "% of" unit should be mantained.
If the size of the selected item is in "pixels", the ruler behaviour should be the actual one.