Render code here, copy it, paste it anywhere. The result carries its own colours inline, so it needs no stylesheet at the destination — which is what makes it work on a site you cannot install a plugin on.
The copy carries two formats. Rich-text editors take the rendered HTML; a code editor
takes the original source, so pasting into one does not give you a screenful of markup.
The theme is fixed when you copy. Inline styles cannot follow the destination's
light/dark setting — pick the mode that suits where it is going.
Some editors strip more than others. Most keep inline style, which is what
this relies on; a few normalise everything away. Paste into a draft before you trust it.
Host CSS. Inline styles beat anything the destination writes at normal weight, but lose
to its !important — and themes do ship
pre { white-space: pre-wrap !important } to stop code scrolling on phones, which
reflows the block. The container defends itself against that already. Switch to
Destination overrides spans only if the colours arrive flattened; it costs about a
quarter more bytes.