Where to insert CSS code for 3 or 4 columns layout

Hi Sebastian,

I would like to start by appreciating the possibility of asking for your support through this forum. Thanks in advance for your assistance.

I am a newbie at tweaking with CSS codes and my initial try at inserting the following code (that you shared as an example in your page here in WordPress’s Theme editor did Not produce successful results yet.

/* 3 column */
.divup-wrap {
    overflow:hidden;
}
.divup {
    float:left;
    width:200px;
    margin-right:20px;
}
.mul-3 {
    margin-right:0;
}

I am using the Optimizepress theme for WOrdpress, and the file I updated adding the piece of code above was the one called style.css
The webpage I am testing out where I have some content between the [divup] shortcodes is this one here:
http://www.rickyricardopereira.com/home-2-3/

I can share that my intention is to create a layout similar to this one here here, except that in this moment I am intending to create 3 OR 4 columns below the video main area only.

Could you please shed some light on where I should insert the CSS code AND if the CSS code should change depending on whether I choose to have a 3 or 4 column layout?

Again, thanks in advance for your assistance.

Cheers,
Ricardo

http://wordpress.org/extend/plugins/divup-content/