How can I change the background of hint boxes in VS Code?

I can't get the box of this tip box (parameter hints) to be transparent. I want to be able to see my code behind it.

^{I posted an image because it would be impossible to show the problem by posting the text, and anyway this isn't a question about the code itself. My question is how to adjust Visual Studio Code window settings.}

I tried to find the setting to change it but its so hard cause there are so many settings.

The colour customization point you are looking for is editorHoverWidget.background. Note that this customization point controls more than just what you've shown in your screenshot (parameter hints). As the name suggests, it controls all editor hover widgets. That includes things like the hover info from hovering the mouse over a symbol, and colour picker hover widgets. I'm not aware of any way to customize only specific types of hover widgets without affecting the other types.

In any case, Ex.

"workbench.colorCustomizations": {
    "editorHoverWidget.background": "#00000000",
    // and some other related ones if you're interested:
    "editorHoverWidget.foreground": "#ff0000",
    "editorHoverWidget.border": "#ff0000",
    "editorHoverWidget.highlightForeground": "#ff0000",
    "editorHoverWidget.statusBarBackground": "#ff0000",
}