In CSS the special variable currentColor gives you access to the current text color of the element. You can use this value in other properties like border-color to automatically adjust the border to match the text color.

CSS
.button {
  border: 1px solid currentColor; /* border color is blue */
  color: blue;
}

.button:hover {
  /* border color automatically changes to darkblue */
  color: darkblue;
}