这样的东西可以单独使用CSS吗？

Is something like this achieveable with CSS alone?

尚未。

如果主题选择器，那么您可以使用：

If the subject selector gets implemented, then you'd be able to use:

!p + h4 {
    ...
}

However that specification is still in an early draft state, so implementation is a ways off. You'd be better off using classes for the time being.