How to change the styles of CTA buttons of email templates

The email template used to notify about new topics have two “Visit Topic” links that I would like to adjust a little bit. Is there a way of changing the styles of both links?

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I wanted to make them both with blue background color and add some padding.

I tried adding CSS by selecting the HTML tags but it does not work. I used the correct selectors (I tested in the browser), but it seems that when the email is generated all styles I added are disregarded.

I tried adding a ‘style’ tag directly into the base template HTML and also tried to using the CSS tab, both ways did not work
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Is there an easy way of changing the styles of that elements?