you must follow the template given to you in the exercise to write a CSS selector.
element {
property: value;
}
If I want to write a css selector that selects the body element for example, then I would write it as follows
body {
}
Then inside the curly braces area I would write the properties and their values.
So the word text-align is a property name and the value is center. text-align: center
that is how you would write that.
Try this exercise again and keep the template in mind as you type.