Changing the appearance of "button ghost"

I am using two types of buttons on my website:
1.
<a class="button" href="xxx">xxx</a>
2.
<a class="smooth-scroll button ghost" href="xxx/">xxx</a>

In the case of number 1, I can change the colour and font in: Appearence / Customize / Colors / Button
But I have no idea how to change the color of number 2. Is there an easy way to give a different color to the border and the text?

Thanks in advance