How do I change the button color of "ask a question"?

To resolve this issue, you can add the following code to the style.css file:

.dwqa-container .dwqa-btn-success {
    background-color: #...;
    border-color: #...;
    color:#...;
}
.dwqa-container .dwqa-btn-success:hover,
.dwqa-container .dwqa-btn-success:focus,
.dwqa-container .dwqa-btn-success:active,
.open .dropdown-toggle.dwqa-container .dwqa-btn-success { 
    background-color: #....;
    border-color: #....;
    color: #...;
    opacity: 1;
}

Hope this helps !