Hi Karim, yep you already did it via custom css

header.navbar-fixed-top {
opacity: 0.8;
}

Also you need to set top margin for layer slider -80px or like this. You’ll see the layer slider settings.

Then it will be like this:

http://imagizer.imageshack.com/img923/2526/7fLTmz.jpg

Hey Karim, here is the LastPoint WordPress theme demo slider settings:

You’ll see the

/*Mobile Layout: 320px. and /*Tablet Layout: 768px. in style.css you should add to some rule for the slider for mobile view.

For this; please go to your Theme Options panel and add those two rules in the custom css area:

/*		Tablet Layout: 768px.
--------------------------------------------------------------------------------------------------*/
@media only screen and (min-width: 768px) and (max-width: 991px) {

	.mainheaderwrapper {
		opacity: 1;
	}
	
	.yoursliderid {
		margin-top: 0;
	}
	
}

@media only screen and (max-width: 900px) {

	.mainheaderwrapper {
		opacity: 1;
	}
	
	.yoursliderid {
		margin-top: 0;
	}
	
}

I hope that will helps to you.