Actually it's very easy to achieve 😃
Step 1 Add JavaScript and html of button in Custom Header.
<script>
document.addEventListener('DOMContentLoaded', function() {
var discussmobilebtn = document.createElement("button");
discussmobilebtn.innerHTML = "Start a Discussion";
discussmobilebtn.onclick = function (event) { document.querySelector('.IndexPage-newDiscussion').click(); }
discussmobilebtn.className += "customdiscussbutton Button Button--primary";
document.querySelector('ul.IndexPage-toolbar-view').appendChild(discussmobilebtn);
}, false);
</script>
Step 2 Add Some Css to shift button to desired position
.customdiscussbutton {
position: absolute;
}
@media screen and (min-width: 750px) {
.customdiscussbutton {
display: none !important;
}
}
That's all Enjoy your new Discussion Button
