The AddToCart component in client/Cart/AddToCart.js takes a product object and a CSS styles object as props from the parent component it is added to. For example, in MERN Marketplace, it is added to a Product view as follows:
<AddToCart cartStyle={classes.addCart} item={this.state.product}/>
The AddToCart component itself displays a cart icon button depending on whether the passed item is in stock or not:
For example, if the item quantity is more than 0, the AddCartIcon is displayed, otherwise the DisabledCartIcon is rendered.
mern-marketplace/client/cart/AddToCart.js:
{this.props.item.quantity >= 0 ? <IconButton color="accent" ...
