Newbie to CSS

Hi,

i am a newbie to CSS. I want to add css class and code to format my tables.
If column 1 row = Geoffnet then the cell should be green
If this cell = Geschlossen then red.

I can add this to CSS of the plugin:
.class {

}
.tablepress .highlight-1 {
color: #81F781;
}
.tablepress .highlight-2 {
color: #F78181;
}

But i am struggling with creating the necessary css class. Where should i do this:
<span class=”highlight-1″>Geoeffnet</span>
<span class=”highlight-2″>Geschlossen</span>

The page I need help with: [log in to see the link]