You can override or customise the default button using css. You can apply the css by using class name or id or default button tag itslef.
Example:
Copy pase the below code between the head tag in your html page.
<style type="text/css">
.yourclass {
-moz-box-shadow:inset 0px 1px 0px 0px #fcf8f2;
-webkit-box-shadow:inset 0px 1px 0px 0px #fcf8f2;
box-shadow:inset 0px 1px 0px 0px #fcf8f2;
background:-webkit-gradient( linear, left top, left bottom, color-stop(0.05, #fae4bd), color-stop(1, #eac380) );
background:-moz-linear-gradient( center top, #fae4bd 5%, #eac380 100% );
filter:progid:DXImageTransform.Microsoft.gradient(startColorstr='#fae4bd', endColorstr='#eac380');
background-color:#fae4bd;
-webkit-border-top-left-radius:0px;
-moz-border-radius-topleft:0px;
border-top-left-radius:0px;
-webkit-border-top-right-radius:0px;
-moz-border-radius-topright:0px;
border-top-right-radius:0px;
-webkit-border-bottom-right-radius:0px;
-moz-border-radius-bottomright:0px;
border-bottom-right-radius:0px;
-webkit-border-bottom-left-radius:0px;
-moz-border-radius-bottomleft:0px;
border-bottom-left-radius:0px;
text-indent:0;
border:1px solid #eeb44f;
display:inline-block;
color:#ffffff;
font-family:Arial;
font-size:15px;
font-weight:bold;
font-style:normal;
height:40px;
line-height:40px;
width:100px;
text-decoration:none;
text-align:center;
text-shadow:1px -21px 0px #cc9f52;
}
.yourclass:hover {
background:-webkit-gradient( linear, left top, left bottom, color-stop(0.05, #eac380), color-stop(1, #fae4bd) );
background:-moz-linear-gradient( center top, #eac380 5%, #fae4bd 100% );
filter:progid:DXImageTransform.Microsoft.gradient(startColorstr='#eac380', endColorstr='#fae4bd');
background-color:#eac380;
}.yourclass:active {
position:relative;
top:1px;
}
</style>
inside the body tag :
<input type="submit" class="yourclass" name="mysubmit" value="Submit">
You can create your own in even in online - http://www.cssbuttongenerator.com/