We are quite restrictive about how much one can change text, simply to keep the styling coherent and clean. That's why various font colors and different kinds of fonts are a no-go!
Use the styling options that are available through the top bar of your textfield and you should be good:
You are probably used to little editors for your text field, nevertheless we will go through the most used and the most misused actions.
don't simply copy/paste text from anywhere, as you copy styling with it. Especially your Office or the internet. If you do this, first copy it to a very basic text editor, where you can not style anything, like Notepad or Gedit, and then copy it again from there to your text field in Campaignion. So you can be sure, no additional unwanted styling messes up your site.
Use the right hierachy in your headings. Heading 2 is more important and bigger than Heading 3 , which is bigger than Heading 4 and so on.
Do not use "bold" to fake a heading. The hierarchy is not only for the visual effect but also important for screen readers and search engines. Also don't use a heading if it doesn't fit the hierarchy just for it's styling.
When adding Images and Videos, use the Media button in your top bar (it looks like a tiny picture).
Do not just copy links and code provided from various websites like youtube. It might seem like it's working, but Campaignion will not know about it; So it's not in your media gallery, not available in your media browser if you want to have it somewhere else too, it messes up styling and is not responsive (won't fit on a mobile screen).
if you know HTML and know what you are doing you can use the "source" button to look at your text in HTML, add additional mark-up and customize your text further.