<!DOCTYPE html>
<html>
<head>
<style>
.button1 {background-color: #4CAF50;} /* Green */
.button2 {background-color: #008CBA;} /* Blue */
.button3 {background-color: #f44336;} /* Red */
.button4 {background-color: #e7e7e7; color: black;} /* Gray */
.button5 {background-color: #555555;} /* Black */
</style>
</head>
<body>
<button class="button1"> button</button>
<button class="button2"> button</button>
<button class="button3"> button</button>
<button class="button4"> button</button>
<button class="button5"> button</button>
</body>
</html>