I am trying to build an website for my college's magazine. I used the "views" module to show a block of static content I created on the front page.
My question is: how can I edit the theme's css so it changes the way that block of static content is displayed?
For reference, here's the link to the site (in portuguese, and with almost zero content for now).
The main css file that drives your content is the styles.css file located in your currently selected theme. In your case that means that most of your site styling is driven by this file: /aroda/roda/themes/garland/style.css with basic coloring effects handled by this file: /aroda/roda/files/color/garland-d3985506/style.css
You're currently using Garland, the default Drupal theme included with the core download, so for best practices you shouldn't edit the included style.css file directly. Instead, you should, as Daniel James said, create a subdirectory in /sites/all called "themes".
If you're using Drupal 6, I'd follow Daniel James directions from there. If you're using Drupal 5, I'd go ahead and copy the garland directory into the themes directory and rename it for something specific to your site (aroda_v1) so you would have something like /sites/all/themes/aroda_v1 which would contain styles.css. At that point, you can edit the styles.css file directly to make any changes you see fit. Hope that helps!