swc / I need a global variable for the duration of the plugin

Question

I am creating an SWC plugin. I will be as brief as possible. The user can style HTML (jsx) elements with attributes.

<div background="red">123</div>

The plugin adds a class attribute with a unique id.

<div className="style642">123</div>

And creates a css file with all found styles

my problem: swc does not allow you to read files. I can't add new styles to css when they are found. I can only completely replace the contents of a file

fs::write("test.css", data).expect("Unable to write file");

I created a global variable

pub struct TransformVisitor {    
    styles:String,
}

When I find the style attribute, I put the style on that line, and write the whole line to a file

But this variable is cleared for each component.

export default function Home() {
    return (
            <>
                 <MyComp></MyComp>
                 <p background={"red"}>123</p>
            </>
   )}

During the processing of "MyComp", the styles of the "Home" component will be removed. Only the styles of one component remain in the file.

Help me please. I need a global variable for the duration of the plugin, or any advice.