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document.getElementById('textboxid').style.height="200px";
document.getElementById('textboxid').style.fontSize="14pt";

//in your CSS file or <style> tag
#textboxid
{
    height:200px;
    font-size:14pt;
}

<!--in your HTML-->
<input id="textboxid" ...>

<input style="height:200px;font-size:14pt;" .....>

<html>
<head>
<style>
.Large
{
    font-size: 16pt;
    height: 50px;
}
</style>
<body>
<input type="text" class="Large">
</body>
</html>

<input type="text" style="font-size:16pt;">

<input type="text" style="font-size:xxpt;height:xxpx">