Como posso alterar o plano de fundo de um determinado tópico?

[JammyDodger]

Receio que minhas habilidades em CSS ainda se limitem a trechos e ajustes, então não sou a melhor pessoa para ensinar nem o básico.

Temos alguns guias que podem ser úteis?

Designer's Guide to getting started with themes in Discourse

So you’re interested in in designing your own theme for Discourse? You’ve arrived at the right topic This guide will be more focused on the SCSS/CSS aspects of working with themes in Discourse. If you are also knowledgeable in JS/EmberJs/Handlebars you can go even deeper by looking into this guide. I will describe to you my personal method’s of designing and theming in Discourse. As with most things, there are LOTS of ways to go about implementing your own designs. I enjoy using the …

Developing Discourse Themes & Theme Components

Discourse Themes and Theme Components can be used to customize the look, feel and functionality of Discourse’s frontend. This section of the developer guides aims to provide all the reference materials you need to develop simple themes for a single site, right up to complex open-source theme components. This introduction aims to provide a map of all the tools and APIs for theme development. If you prefer a step-by-step tutorial for theme development, jump straight to: Themes vs. Theme Compon…