Javascript for font size when user reduces the browser

I made a web site in percentage interest me how to make the letters are proportionate to the size of the Browser when the user reduces the browser. What orders to use for <p> elements. I need javascript examples.

this HTML code:

<!DOCTYPE html>
<html>
<head>
<style>
html, body
{
height: 100%;
width:100%;

}
#telosajta
{
top: auto;
margin: auto;
position: relative;
width: 80%;
height: 100%;
}
.div1
{
border: 1px solid #000;
float: left;
width: 80%;
height:60%;
}
</style>

<body>
<div id=“telosajta”>
<div class=“div1”>
<img src=“slika/slika.png” width=“100%” height=“100%” title=“slika”>
<p>Some text Some text Some text Some text Some text Some text Some text…</p>
</div>
</div>

</body>
</html>