<html>
<body>
<p id="myP" style="background-color:#EEEEEE">
This is the first line if a sample text.
<br>And this is its second line.
</p>
<input type="button"
value="Set lineHeight to 30px"
onclick="myP.style.lineHeight='30px'">
<input type="button"
value="Restore line height to normal"
onclick="myP.style.lineHeight='normal'">
</body>
</html>