The default CSS has many values in px, which is an absolute unit that only reflects the window’s main text size and doesn’t scale for the different elements in the window. This results in inconsistent spacings when, for example, setting different content sizes for the different content sections of the window such as the right-sidebar and references as well as embeds: set the font-size of the references to something smaller, and so many margins and paddings in px will remain the same against what should be a uniform scaling down, causing design distortions.
Relative rendering of blocks could be implemented officially by replacing px with em, for the values to follow the parent elements, so that the block design won’t be affected when the custom CSS sets different font-sizes for the sidebar, references, or embeds.