René (Elevenfour) 
Do you want to add alpha transparency to an opaque hex colour with pure CSS? You can do something like:
.red-60 {
color: rgb(from #ff0000 r g b / .6);
}
This uses the rgb() function to set 60% opacity to the hex value of red.
The letters r g b (note the spaces between) are a representation of the red green and blue values of the hex colour. You can think of them as some sort of variable.
