Ok, I took a look at this, but I haven't tested it in all browsers, so you'll have to see if it works. I make no guarantees -- this is just something I fooled around with a bit today because I had some time.
Make sure to make back up copies of your CSS files before editing them.
Your theme has a complicated scheme of multiple stylesheets -- there's a main one for the layout, and then an additional one for the spring-flavour theme, and some others that seem related to plugins.
My changes below comment out the old lines of the CSS so you can refer back to them if you want to reverse the changes.
Make these changes:
In blix-10/layout.css (line 184 or so). Find #navigation form and replace it with the following:
#navigation form
{
float: right;
height: 100%;
width: 189px;
padding-top: 0pt;
padding-right: 15px;
padding-bottom: 0pt;
padding-left: 15px;
/* EDITED Left border of search form removed */
/* border-left-width: 1px;
border-left-style: solid;
border-left-color: -moz-use-text-color; */
line-height: 0pt;
}
In blixed-10/spring_flavour.css:
line 79 - replace #navigation style with:
#navigation {
/* EDITED changed background color from green to orange */
/* background-color:#A3C159; */
background-color:#FEC42D;
}
line 83 - replace #navigation a with:
#navigation a {
color:white;
/* EDITED added green background to page link buttons */
background: #A3C159;
}
As you see I also put the phrased EDITED in the comments. (Normally I use my own name.) It's a good idea to mark your changes with something you can search for later.
So basically what I've done above is to get rid of the white border on the left of the search bar area, and replaced the whole navigation bar background with the same orange color. But the page link buttons have no background assigned to them unless they are the current page or are being hovered over, so I assigned them a background of the original green of the navigation area. The result is the the orange searchbar background will appear to extend as far left as the buttons.
Again, have not fully tested, but if it doesn't work in all situations, it should at least give you an idea.
If you're planning to start editing the look of your themes, you'll have to start learning CSS. I found this guide indispensable when I was learning:
http://www.westciv.com/style_master/academy/css_tutorial/index.html
(they have plenty of material for free online).
You should also get a decent HTML/CSS editor, that can help. I myself prefer Dreamweaver because I'm used to it, but there are plenty of free ones out there.
Your theme, however, is not an easy one for a beginner in CSS because it has multiple cascading stylesheets.
PS My original assessment of the problem in my first post was incorrect. It doesn't have to do with the padding of the sidebar or content area; the navigation area is separate from those -- it's just designed to line up with what's below.