<!DOCTYPE html>
<html>
<head>
<style>
p.intro::first-letter {
    color: #ff0000;
    font-size:200%;
}  
</style>
</head>
<body>

<p class="intro">This is an introduction.</p>
<p>This is a paragraph with some text. A bit more text even.</p>

</body>
</html>