Untitled

<!DOCTYPE HTML>
<html>
<head>
<style>
body
{ background-color:lightgray; }
#ramka
{ margin-left:auto; margin-right:auto; text-align:center; padding:25px;}

</style>
<script>
function oblicz()
{
var wzrost=document.getElementById("wzr").value;
var waga=document.getElementById("wa").value;
wzrost=parseFloat(wzrost);
waga=parseInt(waga);
if (isNaN(wzrost) || isNaN(waga))
{
alert("zle dane");
return;
}
}
</script>
</head>
<body>
<div id="ramka">
<form action="mailto:sdfsdf@dfsf">
wzrost<input type="text" id="wz"/>
<p></p>
waga &nbsp;<input type="text" id="wa"/>
<p></p>
<input type="button" value="oblicz BMI" onclick="oblicz()"/>
</body>
</html>