CSS OUTLINE COLOR

Outline-color controls the color of an element's outline.

button {
  outline-style: solid;
  outline-width: 2px;
  outline-color: red;
}

You can use different color formats:

outline-color: red;
outline-color: #ff0000;
outline-color: rgb(255, 0, 0);
outline-color: transparent;

Or use the shorthand:

button {
  outline: 2px solid red;
}

Syntax:

outline-color: color;