There is no single code that works in all websites. It depends on the HTML code - can you share it?
Assuming HTML5, use article
selector
The article text is likely in a <article>
tag if the website uses HTML5.
If that is the case you should be able to use:
article a {
text-decoration: none; border-bottom: #EA215A 0.125em solid;
}
Sometimes people put <header>
and/or <footer>
tags within the <article>
tag so the above won't work.
If the HTML output is done well the article probably has sections.
So replacing the selector above with article section a
might give you better results in case header and footer are output within the article.
Without HTML5
You don't have to blindly guess what selector the article content has.
Right click the article text and select inspect element
or similar (likely at the bottom of the context menu).
You can probably build a selector by looking at the tags, which selector will work for article content.
Development tools
Get familiar with the development functionality of your browser in that case.
You will have to make sure this works for all types of pages the site has.
It seems you don't know the HTML too well... time to get familiar with it.