RGBA — Alpha channel as a separate class

Question

Let\'s say we have a list of classes storing background colors.

.bgr-red //background-color: rgb(255, 0, 0);
.bgr-green //background-color: rgb(0, 0 , 255);
         


        

Answer 1

Use CSS variables:

.bgr-red {
  background-color: rgba(255, 0, 0, var(--a, 1));
}

.bgr-green {
  background-color: rgba(0, 0, 255, var(--a, 1));
}

.bgr-blue {
  background-color: rgba(0, 128, 0, var(--a, 1));
}

.alpha-90 {
  --a: 0.9;
}

.alpha-70 {
  --a: 0.7;
}

.alpha-10 {
  --a: 0.1;
}

<div class="bgr-red">...</div>

<div class="bgr-red alpha-70">...</div>

<div class="bgr-red alpha-10">...</div>

And for better support you can consider pseudo element to create the background layer and adjust opacity:

div {
  position: relative;
  z-index: 0;
}

div::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  z-index: -1;
}

.bgr-red::before {
  background-color: rgb(255, 0, 0);
}

.bgr-green::before {
  background-color: rgb(0, 0, 255);
}

.bgr-blue::before {
  background-color: rgb(0, 128, 0);
}

.alpha-90::before {
  opacity: 0.9;
}

.alpha-70::before {
  opacity: 0.7;
}

.alpha-10::before {
  opacity: 0.1;
}

<div class="bgr-red">...</div>

<div class="bgr-red alpha-70">...</div>

<div class="bgr-red alpha-10">...</div>