Ensure we can use < and > characters in modifiers

[RobinMalfait]

This PR will ensure that you can use special characters in modifiers. For example when you want to use <sm:underline where <sm is defined as:

module.exports = {
  theme: {
    extends: {
      screens: {
        '<sm': { max: '399px' },
      },
    },
  },
}

Fixes: #6778