A dynamic modifier capable of automatically generating a rule from a CSS value
(e.g. bg-[rgb(12_12_12)]).
All underscores in the value will be replaced by spaces except in url(), if you really
want to keep one of them, you can prefix it with a backslash \_ and it will be used as
is.
Sometimes the value is ambiguous, for example bg-[var(--foo)] can be handled by either
the background color or the
background size utility. In this case,
you need to provide a CSS type
hint (see the list of hints below) before the arbitrary value. For example
bg-[length:var(--foo)] will generate background-size: var(--foo); (using the
background size utility).