How can I style an IFRAME element that has a constantly changing class name? [closed]

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You can select every iframe, just by writing:

iframe{display:none}

If you have multiple iframes, and this is the only one you want to apply this styling to, you can write something like this:

iframe[src^="//assets.pinterest.com/pidget.html"]{display:none}

Note: Not really a WordPress question, but pure CSS related.