A CSS rule selects specific HTML elements and specifies styling properties for the element. Styling can occur within style tags in the HTML file's header part. Each style rule indicates the element to be styled like h$1($header$1)$ or p $($paragraph$),$ followed by a list in braces $\{\}$ of property:value items like color:blue.

Properties Purpose Example CSS

background$-$color Element's background color

h$1\{$

background$-$color: lightgray;

$\}$

font$-$family Font used for the element's text.

p $\{$

font$-$family: arial;

$\}$

font$-$size Font size used for the element's text.

p $\{$

font$-$size: $9$pt;

$\}$

padding Spacing between element's content and border.

strong $\{$

padding: $5$px;

$\}$

margin Spacing around element $($outside element's border$).$

p $\{$

margin$-$left: $10$px;

$\}$