Add the following code in functions.php

function remove_sf_actions() {
	remove_action( 'storefront_header', 'storefront_header_cart', 60 );
}
add_action( 'init', 'remove_sf_actions' );

And then update the style.css file in theme folder with following or copy this into Customize > Additional CSS

 .woocommerce-active .site-header .main-navigation{
	width:100%;