Info on CSS rules

CSS rules dictate everything's presentation on a page. In fact, HTML does nothing in displaying the page the way you see it. HTML only tells about what certain data on a page should be known as. Even if you do not manually use CSS, it will be computed for you using its defaults, set by the browser.

See the below links for learning CSS:

Codecademy CSS interactive tutorial W3 Schools CSS tutorial

You can implement CSS using the following code:

selector {
  rule_1: rule_value;
  rule_2: rule_value;
  rule_3: rule_value;
}

You can learn about this more in-depth with other tutorials. In this challenge the only CSS changed was about colours.