@tristan-breon-1 if you are on a premium account and in the classic editor you can go to your dashboard and click Settings > Custom Code
In the custom code area click add new then you can code your css there
<style>
//Your css here...
//Something like
a{
color: #FF000;
}
</style>
You might need to add the !important flag to the css if the override doesn’t work. I would caution to thoroughly check your site as what I added above will override ALL links so possibly will have unintended consequences.
You can load the code on every page or only on certain pages and make sure to mark the code as essential
Publish your site and refresh the page and you should see your changes.
Alternatively, if you are just starting you may want to consider looking at EditorX which has more design versatility.