The css property defines the style of the targeted element and consists of a name and a value.
h1 { color: red }
For example: by using the "color" property, you can define the text color of the targeted element.
When you want to define more then 1 property, then you need to separate them by a semicolon.
h1 { color: red; text-size: 20px;}
Where to put it
Inside the style attribute of the element
<h1 style="color:red;">Some text</h1>
In the document head inside a style tag
<head>
<style type="text/css">
h1 { color: red; }
</style>
</head>
In an external css file
You can place all the css rules in an external file that you then can link to.
<link rel="stylesheet" type="text/css" href="/externalcssfile.css">