https://www.w3.org/TR/css3-selectors/
Note that the length of the first line depends on a number of factors, including the width of the page, the font size, etc.
<style>
P::first-line {
text-transform: uppercase;
color: red;
}
</style>
<body>
<P>This is a somewhat long HTML
paragraph that will be broken into several
lines. The first line will be identified
by a fictional tag sequence. The other lines
will be treated as ordinary lines in the
paragraph.</P>
<P>This is a somewhat long HTML
paragraph that will be broken into several
lines. The first line will be identified
by a fictional tag sequence. The other lines
will be treated as ordinary lines in the
paragraph.</P>
https://developer.mozilla.org/en-US/docs/Web/CSS/text-transform
