We do enjoy helping people with their free, open source Discourse instances, and that is indeed part of our responsibility to the open source community.
However:
Over time, there has been a constant influx of basic HTML and CSS questions that are taking time away from us helping with more substantive issues specific to Discourse.
It’s not a productive use of our time to teach basic HTML and CSS. There are thousands of online resources that describe how to make changes on an HTML page with a few CSS rules. We would much rather spend that time troubleshooting Discourse and improving Discourse for you.
Furthermore, these topics tend to be very specific to the particular needs of particular sites and not very generalizable or helpful to future visitors who might stumble upon that topic.
So from this point on, we will be closing any questions about rudimentary HTML and CSS changes, instead pointing them to a general Discourse topic that describes how to use the F12 key in your browser to find HTML targets, and how to add basic CSS lines to your site customization, with a few examples, and maybe links to public HTML and CSS tutorials elsewhere on the web.
These questions will also be marked for auto-deletion after 24 hours.
(Note that if you are a Discourse hosted customer, we are much more open to assisting with these kinds of tasks, within the time constraints of your particular hosting plan.)
Meta is not a dedicated support site for a complete guide to getting started with CSS — just like it is not a dedicated support site for learning Ruby and JavaScript completely from scratch, if you wanted to start customising the behaviour of Discourse through plugins.
If you want to customise the appearance of Discourse, you will need to learn more about CSS.
There are guides here on making themes, theme components and plugins which are specific to Discourse, but not for learning to be fluent in CSS or Ruby totally from scratch, since that’s a general skill. Sometimes people have time to kindly help, but it’s not always going to be possible, because it means having to go through general HTML & CSS knowledge – the basics of the Inspector and classes and properties etc.
This guide linked above can help you get started, as well as the Beginner’s guide to developing Discourse Themes:
If you would like to make extensive customisations — or maybe you just don’t have the time to learn as well — another option is also to post in the marketplace.