Composes keyword geting error as unknown property in vs code

Question

In my application i have created a custom.css file which i am using through compose keyword in App.js file but it is giving error of unknown property. Please suggest me what can i do to resolve this

 

custom.css

.button{
    color: white;
    border: 3px solid gray;
    background-color: black;
}

App.css

.submitButton{
  composes: App;
}