Hi Monique,
First add below code in your page editor
<a class="call-to-action my-button" href="button-link-here" title="Button Title">Button</a>
and then Go to Appearance -> Customize -> Ambition Theme Options -> Custom CSS and paste the below CSS code then click on Save button.
.call-to-action.my-button {
background-color: #89a452;
border: 1px solid #89a452;
color: #fff;
}
Note: Change above HEX color code #89a452
to your own HEX color code.
Thank you!