We can mix Internal and Inline Styles.
In this case the Inline style overrides the Internal style stored in the head.
<head>
<style type='text/css'>
.billy {background-color:tan;color:sienna;font-size:16pt;border-style:ridge;}
</style>
</head>
<body>
This <span class='billy' style="background-color:blue; color:yellow;" > text </span> was formatted with a billy Class definition
But overwritten with an inline style<p>
This text just uses the billy class to <span class ='billy'>display text</span>
</body>
This text was formatted with a billy Class definition
but the colours have been overwritten with an inline style.
This text just uses the billy class to display text