Hi there,
I believe what David meant was, your site already has the CSS that makes the post display in a row-like manner.
He’s asking if that’s already fine by your requirement, else you can remove it.
That CSS he’s pertaining makes the posts display in rows on mobile. You can keep it if it’s fine working for you already.
My suggestion would be to atleast increase the @media rule from @media(max-width: 500px)
to @media(max-width: 768px)
so it catches all mobile.
I see that your site has excerpt hidden on mobile while the reference site had it visible. Do you want to change this as well? If yes, we may have to use some PHP snippets to change the HTML structure a bit.