site categories css- rows and columns for sub categories

I see how I can change the site categories landing page to the number of rows and columns that I want, great.

Now I want to change the sub category results to the same number of columns across the page.

I tried this in my theme's css{
margin: 0;
padding: 0;
width: 600px;
min-height: 300px;
#site-categories-wrapper .site-categories-list li{
display: block;
float: left;
width: 180px;

but I came up with bupkus.

What am I doing wrong?