changing background color of home page only in Selene wordpress theme

I have to change the background color of ‘home page and its text’ in a website based on Selene wordpress theme. Currently, I can do this through page-id of home page in following way from style.css:

/*home page background color*/
.page-id-18 #container {
     background: #000000 !important;
 }

/*home page text color*/
.page-id-18 h2 {
     color: #000000 !important;
 }

Is it right to do or there is other way? Also I have heard that using !important property should be avoided, is it wrong then?