using style.css in child theme

Hi there,

I am trying to add custom css to the style.css in child theme, but it seems that anything I add in there is not being used by the site.

e.g. .content-box-green {
margin-bottom: 30px;
margin-left: 15%;
margin-right: 15%;
overflow: hidden;
padding: 30px;
background-color: #19d079;
color: #fff;
border-radius: 5px;
}

If I add that to Appearance>customize>addition CSS it works fine. But If I add it to the child theme style.CSS it does nothing.

Do I need to do anything else to get the theme to use my custom CSS?