Hi,

Please go to themesetting => Custom CSS code :

Add the following code:

header.parallax {
   background-size: cover!important;
}
@media (max-width: 768px){
   well-come.f-60 {
       font-size: 40px!important;
   }
   .well-come.rotate-text.m-b-100 {
       margin-bottom: 40px!important;
   }
}
@media (max-width: 480px){
   .intro-message.m-t-0{
       margin-top: 30px!important; 
   }
}