Bad responsive

I want to make the website fully rubber, responsive.
I installed:

Fluid Width (full screen) - ON
Responsive Behaviour - Enabled
Responsive Menu - Enabled

Applied the standard layout left - content - right.

If the browser window is stretched to full screen, all three positions shows normally

But if reduce the window by about one-third left and right positions receive additional padding from the edge of the screen.
Demonstration site sparky.hol.es/index.php/web-design .
Can you explain to me why is this happening?

As I see only problem is login module, in template_css.php is several places you will find:

.span2 {
width:XXXpx;
}

increase values

This change does not work. Probably need to change radically the template to the window was stretched to the full width for all gadgets!
See attachment.

you need also to decrease width of central area .span8 for double amount you increase .span2 width.

Left and right column have class span2 and central span8 so total sum is .span2 + .span8 + .span2

Sorry. Something I do not understand. After all, I need a responsive (rubber) version, and you suggest I set the size in pixels ...

Yes but you see definition are for different @media-screen sizes