grid-focus sidebar sizes customization

I have grid-focus theme up and running.

I have two sidebars (two columns) I would like to have different widths for these sidebars. is this possible?

I tried to change

.secondaryColumn {
float: left;
margin: 28px 0 0 20px;
overflow: hidden;
width: 188px;
float:left;
line-height:1.3em;
padding:7px 10px 0px 7px;
}

the width ‘188’ but it changes the size on both sidebars simultaneously.

the following third-column options doesnt make any changes to the size

.thirdColumn {

float: left;
margin: 28px 0 0 22px;
overflow: hidden;
width: 240px;

}

I am a beginner and would appreciate if someone can help me with this.