CSS ?ver=4.7.3 not found

If your file working without query string then you can remove the query string by adding the following into functions.php

// Remove WP Version From Styles    
add_filter( 'style_loader_src', 'sdt_remove_ver_css_js', 9999 );
add_filter( 'script_loader_src', 'sdt_remove_ver_css_js', 9999 );

// Function to remove version numbers
function sdt_remove_ver_css_js( $src ) {
    if ( strpos( $src, 'ver=" ) )
        $src = remove_query_arg( "ver', $src );
    return $src;
}

or you can try a plugin which does same. Remove Query Strings From Static Resources