Use font-weight css property, to set the thickness or boldness of a font.

Bold font weight Example

<html>
<head>
<style>
div {
   font-weight: bold;
}
</style>
</head>
<body>
<div>
 font weight as bold example
</div>
</body>
</html>

Normal font weight Example

<html>
<head>
<style>
div {
   font-weight: normal;
}
</style>
</head>
<body>
<div>
 font weight as normal example
</div>
</body>
</html>