how to change the color in css for an outline button bootstrap code example

Example 1: bootstrap Outline buttons

In need of a button, but not the hefty background colors they bring? 
Replace the default modifier classes with the .btn-outline-* ones to 
remove all background images and colors on any button.

<button type="button" class="btn btn-outline-primary">Primary</button>
<button type="button" class="btn btn-outline-secondary">Secondary</button>
<button type="button" class="btn btn-outline-success">Success</button>
<button type="button" class="btn btn-outline-danger">Danger</button>
<button type="button" class="btn btn-outline-warning">Warning</button>
<button type="button" class="btn btn-outline-info">Info</button>
<button type="button" class="btn btn-outline-light">Light</button>
<button type="button" class="btn btn-outline-dark">Dark</button>

Example 2: bootstrap button outline

<button type="button" class="btn btn-outline-primary" href="#">Primary</button>