Problems modifying Wind theme CSS

This is my first post, and it's a long one. Let me know if this is not posted in the right place. After crashing my installation trying different themes, I decided to try twigging the default Wind theme to my satisfaction. I've been fairly successful, as you can see if you visit campbellphoto.ca/gallery. I can provide the CSS changes I made if anyone is interested. Anyway, I ran into a road block trying to change the background of a few widgets - Next Page, Previous Page, Add a Comment & View More Information. All these widgets are visible at http://campbellphoto.ca/gallery/index.php/Now_Showing/CC-20101014-001

I was able with Firebug and Web Developer to find and change the CSS for the desired result on the fly. Unfortunately, they only provide the generated CSS, not the actual CSS documents. I found what I thought was the applicable code and made the following changes in

THEMES/WIND/CSS/THEMEROLLER/ui.theme.css

/* Interaction states----------------------------------*/

FROM:

.ui-state-default, .ui-widget-content .ui-state-default { border: 1px solid #c5dbec; background: #dfeffc url
(images/ui-bg_glass_85_dfeffc_1x400.png) 50% 50% repeat-x; ...}
...

.ui-state-hover, .ui-widget-content .ui-state-hover, .ui-state-focus, .ui-widget-content .ui-state-focus { border: 1px solid #79b7e7; background: #d0e5f5 url(images/ui-bg_glass_75_d0e5f5_1x400.png) 50% 50% repeat-x; ...}

TO:

.ui-state-default, .ui-widget-content .ui-state-default { border: 1px solid #c5dbec; background-color: #444; ...}
...

.ui-state-hover, .ui-widget-content .ui-state-hover, .ui-state-focus, .ui-widget-content .ui-state-focus { border: 1px solid #79b7e7; background-color: #666; ...}

I uploaded the modified ui,theme.css file, but it has no effect, even after reloading the page. Firebug & Web Developer still show the default CSS. Can anyone tell me why I'm not getting the results I want? Is there another file somewhere which is overriding this one? I've changed the matching file in admin_wind, but that produces no change either. Disclosure: My knowledge of CSS is rudimentary and PHP is a big mystery to me.

Thanks Dave. That worked. Here's the code I added to the bottom of screen.css:

.g-button {
background-color: #444 !important;
background-image: none;
}

.g-button:hover {
background-color: #666 !important;
background-image: none;
}

I will take your advise to create my own theme before doing any upgrades - as soon as I figure out how to do it. I'd be willing to share it with the community if there is interest - and when I learn how.

I'm sure I'll be back with more questions - AND HERE'S ONE NOW: Is there anything posted on customizing the header/banner? I would like either a larger font or placing a larger logo than the default Gallery one.