Uppercase the text in CSS in web development

What is the difference between uppercase and lowercase?

Upper Case: THIS IS UPPER CASE

Lower Case:  this is lower case

Example:

<html>
<head>
<style>
.height_set
{
text-transform: uppercase;
}.forLower
{
text-transform: uppercase;
}

.forCapitalize
text-transform: capitalize;
}
</style>
</head>
<body>
<div class=”forUpper”>THIS IS UPPER CASE REPRESENTATION.</div>

<div class=”forLower”>this is lower case representation.</div>

<div class=”forCapitalize”>this is capitalize representation.</div></h1>
</body>
</html>

Output:

THIS IS UPPER CASE REPRESENTATION

this is lower case representation.

This Is Capitalize Representation.