Learning to create a custom CSS for your web page is a bit much for this forum. However, I put together an example web page that shows how a custom submit button could be made - you would use this in place of the PayPal graphics if that's what you have in mind.
Just copy the example to a blank page - you could even use NotePad for example. Open Notepad, copy the code below and paste it into Notepad, then save the file as Test.html. You then use your web browser to open the Test.html file.
<!doctype html>
<html lang="en">
<head>
<title>TEST CSS EXAMPLE</title>
<!-- START META TAG SECTION -->
<meta name="Description" content="TEST">
<meta name="KeyWords" content="EXAMPLE">
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
<meta name="revisit-after" content="5 days">
<meta name="robots" content="index, follow">
<meta name="rating" content="general">
<meta http-equiv="Cache-Control" content="max-age=200">
<!-- START STYLE SHEET OR CSS SECTION -->
<style media="screen" type="text/css">
input[type=submit].button-order
{
color: #FFFFFF;
font: bold 14px arial, serif;
text-align: center;
background-color: #2244FF;
padding: 7px 5px 7px 5px;
margin: 4px 0px 2px 0px;
cursor : pointer;
width: 115px;
-webkit-appearance: none;
border: #000000 0px solid;
/* CORNER ROUNDING */
-moz-border-radius: 5px;
-webkit-border-radius: 5px;
-khtml-border-radius: 5px;
border-radius: 5px;
}
input[type=submit].button-order:hover
{
color: #FFFFFF;
background-color: #089608;
border: #000000 0px solid;
}
</style>
<!-- END STYLE SHEET OR CSS SECTION -->
</head>
<body>
<br><br><br><br><br><br><br>
<!-- START OF FORM -->
<form>
<div align="center">
<input type="submit" value="Donation" class="button-order">
</div>
</form>
<!-- END OF FORM -->
</body>
</html>
