Opacity settings and slider

hi, i’ve added this custom CSS:

.container {
    opacity:0.88;
    }

.main-slider-container {
   opacity: 1;
   }

.head-container {
    opacity:0.97;
    }

in order to display the main content with a bit of transparency on the background.

but the images in the slider are a bit transparent too.

how can i leave the slider non-transparent?

thank you