Generating a css gradient with single color

I am trying to generate a gradient using one single color and then varying the brightness or some other related variable.

Is it possible to do so ?

You can use alpha channel for this purpose. Consider color "#428383":

div {
  background-color: #428383; /* for browsers without gradient support */
  background: linear-gradient(#42838344, #428383ff);
  width: 100px;
  height: 100px;
}

<div></div>