Why add tags as classes in article

Sure, what you can do with these CSS classes is write CSS that will be used only on the posts that output that CSS.

For example you could change the font color and size with this:

.tag-pigment-2 {
font-size: 24px; //really big font
color: blue; //blue font
}

You can then have a custom look for each tag. Your best bet for more on this is to consult the theme provider.

To discover what CSS is output by your theme, use a web inspection tool such as Firebug: https://getfirebug.com/ , Chrome Inspect Element: https://developers.google.com/chrome-developer-tools/ or Internet Explorer 9+ F12 Dev. Tools: https://msdn.microsoft.com/en-us/library/dd565627(v=vs.85).aspx#csstool

There are others.

When editing CSS, use a Child Theme
https://codex.www.ads-software.com/Child_Themes
Custom CSS Plugin, or Theme provided custom CSS option.
Edits to parent themes are lost on theme update.

Learn CSS: https://www.w3schools.com/css/

wow, that was a quick response!
Thanks!

I didn’t think of the possibility to style a class made of a specific tag, since there are quite many of them… but, well, it seems like that’s a huge playground …

best
david