Have you tried to clear the cache in front-end? (ctrl+shift+F5 if you are using google chrome).
Or you can force you style using the !important attribute like this.
.hikashop_product_description_main{
background-color: darkturquoise !important;
color: white !important;
padding-left: 4px !important;
padding-right: 4px !important;
}
Or, if this is
the Template
you are talking about, try to applay the style to the ID and not to class, with or without " !important " attribute.
div#hikashop_product_description_main{
background-color: darkturquoise;
color: white;
padding-left: 4px;
padding-right: 4px;
}