<!DOCTYPE html>  
<head>
<script src="calculator.js"></script> 
<title>Calculator</title>  
<link rel="shortcut icon" href="http://www2.uah.es/biomodel/lab/mapa-peptidos/calc.gif" /> 
<link rel="stylesheet" href="calculator.css" />
</head> 
<body>   
<div align="center"> 
<table border="2" cellspacing="2" cellpadding="5" > 
<form name="myFormulary">  
<tr> 
<td> 
<label><font color="white">Number</font></label> 
<input type="text" name="number1" size="20"> 
<br> 
<label><font color="white">Number</font></label> 
<input type="text" name="number2" size="20"> 
</td> 
</tr> 
<tr> 
<td align="right"> 
<label><font color="red">Result</font></label> 
<input type="text" name="result" size="20" disabled> 
</td> 
</tr> 
<tr> 
<td align="center"> 
<input type="button" value="+" onclick="add()"> 
<input type="reset" value="Erase"> 
</td> 
</tr> 
</form> 
</table> 
</div> 
</body> 
</html>

<!DOCTYPE html>  
<head>
<script src="calculator.js"></script> 
<title>Calculator</title>  
<link rel="shortcut icon" href="http://www2.uah.es/biomodel/lab/mapa-peptidos/calc.gif" /> 
<link rel="stylesheet" href="calculator.css" />
</head> 
<body>   
<div align="center"> 
<table border="2" cellspacing="2" cellpadding="5" > 
<form name="myFormulary">  
<tr> 
<td> 
<label><font color="white"><strong>Number</strong></font></label> 
<input type="text" name="number1" size="20"> 
<br> 
<label><font color="white"><strong>Number</strong></font></label> 
<input type="text" name="number2" size="20"> 
</td> 
</tr> 
<tr> 
<td align="right"> 
<label><font color="red"><strong>Result</strong></font></label> 
<input type="text" name="result" size="20" disabled> 
</td> 
</tr> 
<tr> 
<td align="center"> 
<input type="button" value="+" onclick="add()"> 
<input type="reset" value="Erase"> 
</td> 
</tr> 
</form> 
</table> 
</div> 
</body> 
</html>

Add <strong> to: 'Number & Result'.
Add <strong> to: 'Number & Result'.