Style to denote not tagged

How can I apply custom styling to the line which doesn’t contain specfic tag?

I don’t think you can directly…

But I think you can indirectly by just setting that style over the entire document. And then when a line has a tag (which you can style) set it to normal style? For example this style will make all items that are not tagged with @test red:

item {
  color: red;

item[data-test] {
  color: black;