Help needed with adding a class to p.url from a page collection

Hi all, I am a newbie with Grav (and Twig) and have what is perhaps a daft question so apologies in advance.

I've been learning bit by bit and have a healthy enough starting point with this collection...

{% for p in page.collection.order('folder','asc') %}
###{{ p.title }}
{% set showcase_image = p.media.images|first.cropZoom(450,200) %}
[{{ showcase_image.html(p.title,p.title) }}]({{ p.url }})
{{p.summary(250)}}
[Find out more]({{ p.url }})
{% endfor %}

However, I want to add a class to p.url

I've tried a few things including appending this ?classes=button,big to {{p.url}} but nothing works.

Can someone please help me out/ point me in the right direction? Any help would be much appreciated

Where are you adding that code?

Twig is mainly for templating, perhaps you don't need markdown syntax just use twig and html:

{% for p in page.collection.order(‘folder’,‘asc’) %}
    <h3>{{ p.title }}</h3>
    {% set showcase_image = p.media.images|first.cropZoom(450,200) %}
    <a href="{{ p.url }}">
        <img src="showcase_image.url" alt="{{p.title}}" />
    </a>
    {{ p.summary(250) }}
    <a href="{{ p.url }}">Find out more</a>
{% endfor %}

Many thanks - this has really helped!