Customize +/- slider

[admin]

Border color can be changed like this:

Code:

.control-spinner .btn {
  background-color: #f90;
  background-image: none;
  border-color: #f0f;
}

.control-spinner input {
  border-color: #f0f;
}

The whole visualization is just HTML/CSS/JS. Any tutorial on basic web front-end development can be applied here.