Let me start by saying I have very little web development experience, but a coworker steered me to this framework when I was considering Joomla.  So far, I think this is the right choice, from what I've seen so far. 

About my skin choice...  For now, money is tight, as my wife and I are supporting a disabled adult son, and I have this web idea that I'm hoping may bring in some extra money.  If it does, then money won't be so tight, but for the moment, buying a license for Artisteer is out of the question.  We just can't afford that.  So looking through the default skins, I've found that the jQuery-ui skin is the closest to what I'm looking for.  There are only three things I want changed.  Get rid of the picker that lets the user choose different skins within the jQuery-ui and go with just the Redmond theme, get rid of the wave/split color on the headers and go with one color, and get rid of the rounded corners and make them square. 

I've been successful on two of these fronts.  I commented out this line in Layout.Master to get rid of the picker:
<portal:JQueryUIThemePicker ID="tp1" runat="server" AutoPostback="true" RenderAsListItem="true" />

I copied the images from ajax.googleapis.blahblahblah and created my own Images folder at /Data/Sites/1/skins/jqueryui-1/Images and put the images in that folder, including the modified ui-bg_gloss-wave_55_5c9ccc_500x100.png that is now just one color.

I've added <file>jquery-ui.css</file> to the style.config file.

I've copied the jquery-ui.css file from ajax.googleapis.blahblahblah and put it in my /Data/Sites/1/skins/jqueryui-1 folder, and in the corner radius section I've changed all of the radii to 0px (from 5px).

It seems like this is all that I should need to do.  But it doesn't work.  The result is that my site now uses my images, but the corners are still rounded, and when I hit F12, the CSS is coming from ajax.googleapis.blahblahblah.  I'm confused, since the jquery-ui.css is what is telling it where to look for the images, and it is finding them correctly, but that same file says 0px for corners, but that is coming from the google copy.  I would think there should be a much easier way to override this.

I've already considered that I could download jqueryui and the javascript and such that I found in the directions on how to run mojoPortal on an intranet without internet access, but it seems overkill to do all that just because I don't know what I'm doing on a lousy skin.....    Surely I'm just overlooking something really simple...  Any help is very much appreciated.

The site is "online" with the offline message, at www.win8appsnow.com.  But I believe it is resolved.  Must have been my browser cache fooling me because all of a sudden it started working.  :/

Thanks, Isaac.  I appreciate all your help.  I'll take a look.