Changing the Submit button colour on comments form

All I want to do is change the Submit button on my comments form. My comments.php is in a child theme and says this:

<?php
$args = array(
	'title_reply'			=>	__( 'Discuss this request' ),
	'logged_in_as' 			=>	'',
	'label_submit'      	=>	__( 'Post Message' )
);
comment_form($args); ?>

The class is (so the tutorial I’m reading says) #submit, so I have this in my style.css:

#submit  {
color: #FFFFFF;
font-size: 1.1em;
font-weight: normal;
line-height: 1.4em;
margin-top: 5px;
border: 2px solid #2AB574;
border-radius: 5px;
padding: 5px 5px;
text-align: center;
text-decoration: none;
display: inline-block;
background: #2AB574;
}

And the button is blue, not green. Bizarrely, it takes every other piece of information in the style, but not the background colour. I’ve tried it with background-color as well, no dice. It’s driving me insane. I’ve read the Codex, which is outdated, incomplete and unhelpful (as usual).

Any pointers on where it could be inheriting that annoying blue from and how to stop it happening would be great. Thanks!