Hello Khalil,

You have to go wp-admin >> Theme >> negocio-business-pro >> style.css >> Find below class and change background
overlay as you want.

1. FOR HEADER SLIDER

.ht-slide-overlay {
background: rgba(0,0,0,0.4);
}

2. FOR FOOTER

#ht-colophon .overlay {
background-color: rgba(0,0,0,0.8);
}

Thank You.