elements.) In CSS, you choose which properties you want to affect in your rule.
Property value
To the right of the property after the colon, we have the property value, which chooses one out of many possible appearances for a given property (there are many color values besides red).
Note the other important parts of the syntax:

Each rule set (apart from the selector) must be wrapped in curly braces ({}).
Within each declaration, you must use a colon (:) to separate the property from its values.
Within each rule set, you must use a semicolon (;) to separate each declaration from the next one.
So to modify multiple property values at once, you just need to write them separated by semicolons, like this:

p {
color: red;
width: 500px;
border: 1px solid black;
}