CSS (Cascading Style Sheets) is a language that allows us to define the style and positioning of HTML elements within a web page. With it we can change, for example, the font, color, size and layout of our content. It also allows us to add anzimations and interactivity to elements.

In the same way HTML, CSS is not a programming language, but a style language. It allows us to access page elements and control their appearance through a well-defined set of rules (ruleset). For example, we wanted to change the color of a title <h1> :

h1 {
  color:blue;
}

What we have just seen is an example of a CSS rule. It consists of a selector (h1) that allows us to define what we want to select within the web page (Elements, classes, id, etc.), the declaration (color:blue) that is the set of properties that will be modified, the properties(color) that is the specific characteristics of each element possible to be modified and finally the property value(blue) that is one among the possible style options for each property (e.g. a color for the color property or a number for the font-size property). At the end of each declaration you need to add a semicolumn; .

Additional Technical Documentation

• CSS on MDN Web Docs

• CSS Tricks