For the first gallery on your page, try changing:
<div id="juicebox-container"></div>
... to:
<div id="juicebox-container" style="float: left;"></div>
This should hopefully position your gallery below your text (without a large gap) and allow you to increase the spacing in your side menu.
Incidentally, you have several <div id="themes"> entries on your web page. Each id on a web page should be unique.
If you need to apply CSS rules to multiple elements, you should use classes instead of ids.
Please see this web page for details.
Also, I would recommend not using universal CSS such as the following in your 'main.css' file.
* {
margin:0px;
padding:0px;
border:0px;
}
Such rules will apply to all elements on your web page including those in your galleries. The galleries have no choice but to inherit these rules. Try to apply CSS rules to only those elements on your page which specifically require them through use of classes and ids.