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;
}