Change background color for certain widgets.

Hello,
Here is the link of my site.

I wants change background colors of widgets with different colors?
I had used a theme name ‘Suffusion’ and had inserted some CSS to change background color.

One of the CSS is

#ctc-2 { border: none; background: #2db10f; }

where ctc-2 is a aside id of widget.

After installing new theme, I copied widget ID from page source and created a CSS but it is not showing any changes.

What should I do?
Please explain in details as I am noob into web languages.