There is no point of using hex in content
because if you insert it by sheet.insertRule(rule),
then hex numbers will be shown as normal chars
in elements tab.

Note, if you directly write a CSS rule in a webpage,
then hex numbers will remain as it is even in
elements tab of DevTools

[Important] 
If you use a variable, it maintains hex number in element tab!
{
	--id6: "\591a\91cf\306e\672c";
	content: var(--id6);
}

This is a test

これは 多量の本 です。