How to remove a rule in css regex?

Question

css

Good day. Can you please tell me how to remove unnamed rules in css with a regular expression?
Example:

{
  color: red;
}

I wrote a regular expression
/((\n|\s{2,3})\{)(.+?)\}/is
. It works, but it also removes such rules.

a
{
color: red
}

Answer 1

https://regex101.com/r/OFX59Z/7
Here you can change the number of hyphens after the defining selector by duplicating [\w)] with \s added inside the "look-back" group (?<!). And in [\w)] add some more characters to prevent deletion.