Annoying Blue Color For Button In HTML

Screen shot of problem I am trying to get rid of this annoying blue color in my Bootstrap button supported with Bootstrap. First, there was an underline with blue color, but when add text-decoration: none underline is cleared but still blue color.

<style type="text/css">
      a, a:link, a:visited, a:hover { text-decoration:none; }
      </style>



      <button type="button" class="btn btn-outline-dark">
            <a target="_blank" rel="nofollow noreferrer" href="https://www.instagram.com/freyahomebodrum_mertticaret/"
              target="_blank">Instagram</a>
          </button>

But I still have the blue color as in the screenshot. I have tried variations using span but that does not help either. Am I doing something wrong above?

Thank you in advance.

try this change the color property of anchor tag like this.

a{
 color: #000; /* this will change the color to black
}