Image alignment not working

I installed a new theme in my blog, so I noticed the image alignment and captions were not working, so I added the code to do this:

WordPress Generated Classes

But it doesn’t work !!!!

I tried almost everything, but it the image alignment and wordpress captions aren’t working.

This is the CSS file: http://blog.lomasinteresante.net/wp-content/themes/diseno/style.css
Other CSS code I added to the theme aren’t working neither:

.download {
	background: #D0F29D url('http://blog.lomasinteresante.net/wp-content/themes/k2/images/download.jpg') 10px center no-repeat;
	border-top: 2px solid #9CD941;
	border-bottom: 2px solid #9CD941;
	padding: 10px 10px 10px 52px;
	text-align: center;
	line-height: normal;
	}

Here is an example of both codes (img alingment and .download):

http://blog.lomasinteresante.net/descargas/puestas-de-sol-wallpapers.html

(A green box should appear were it says “::Descargar::”)

So, can any one tell me why the CSS codes aren’t working and how to fix this ? Thanks

(Yes, my english sucks!)