I do like Gutenberg, the “next-gen” WordPress editor. Yet it is still in its infancy as there are many little graphical customization that its basic blocks does not allow for. Neither the old editor allowed them, I must acknoledge, but you could switch to the HTML code and add a
<div style="border: red double thick;"> to get something like
I could keep doing it but I would have lost all the ease-of-use that Gutenberg bring us. So a quick search with my favourite duck told me to try “Multipurpose Gutenberg Block” as it allow to define borders, padding, background gradients and so on.
I hope all those features will come to basic Gutenberg blocks. But they won’t be “basic” anymore and most probably they won’t came as all those features would add too many sliders and options to the “paragraph” block.
Many WordPress developers would not like all that complexity as it is often unneeded. And unneeded complexity makes software harder to use and slower.
I also suspect that those borders aren’t stylish enough, according to “modern webpage typesetting”. Oh, all those fashions! Don’t show pages like “Space Jam” to young web developers: they could die on the spot for the shock!