Background Opacity No RGBA for Sass - html

Question

Is there a way to make my background transparent without using RGBA so that I can change the color using Sass variables later without making the contained text transparent?
$dark: #000;
$highlight: blue;
nav {
width:100%;
background: $dark;
opacity: .5;
ul {
li {
margin: 0 3%;
a {
display: block;
font-size: 1.4em;
&:hover {
color:$highlight;
}
}
}
}
}

Answer 1

You can use Sass functions to add transparency to a color.
background: rgba($dark, 0.5);
or
background: transparentize($dark, 0.5);
or
background: fade-out($dark, 0.5);
Sass has lots of handy functions for manipulating colors, strings, numbers, selectors, and more.

Answer 2

Makes not much sense to not use rgba.
Both opacity and rgba() are not supported by IE8, just 9 and above (if you are required to support it). With the exception that IE8 accepts the filter, that can be somewhat of a workaround to transparency.
If that isn't the case, and you simply don't want to use because it's annoying to convert hex to rgb, (which I too find annoying), no fear! SASS accepts a HEX #000 as a value for rgba and converts it properly, like this:
$dark: #000;
background-color: rgba($dark, .5); //outputs background-color: rgba(0,0,0,.5); in this case
But anyways, here is an approach with pseudo-elements after/before (you choose). Refer to the comments:
$dark: #000;
$highlight: blue;
nav {
width:100%;
background-color: transparent; //transparent or you won't see the color behind!
//needs to be relative or after will go outside nav bounds
position: relative;
z-index: 0;
//using after (or before) to fake the bg
&::after { //if you need to support IE8, use single colon instead. Standard is :: but IE8 just supports with one
content:"";
display: block;
//those two really could be just be
//"background-color: rgba($dark, .5);" you know
background: $dark;
opacity: .5;
//filter here if you want IE8 support
//making it fill entire nav
bottom: 0;
top: 0;
left: 0;
right: 0;
position: absolute;
//behind our nav
z-index: -1;
}
//ul and so on here
}

Answer 3

you can use RGBA with sass. Why do you not want to use RGBA?
background: rgba(0,0,0,0.5);