In CSS, every property has what’s referred to as an initial value. Sometimes this is called the default value, but the spec uses the term initial, which I think is a slightly better term.
Technically speaking, the initial value of any given property needs to be declared only if that value is overriding a previously-defined value that’s not the initial value. But initial values are often present even when they’re not necessary.
For example, suppose I have a block-level element that I want to take up the full width of its parent. I want it to sit on its own “line”, so to speak, in the layout, so I add the following CSS: