In a CSS document, within what must you enclose properties and values when you define a rule for a specified selector?

Curly Braces {}.

Explanation:

The syntax for writing a CSS is as following:-

selector {

property : value;

}

CSS is used for providing the style to the HTML page. Such as fonts, background, height, width etc.

For example:

h1{

font:20px;

background:red;

}

The above written CSS is for the h1 tag in HTML. The font size will be 20 pixels and background color will be red.

So we can say that we need to enclose properties and values in curly braces.