I’ll raise your improvement with a unicode emoji
settingsBtn.textContent = '⚙️';
A few more additions:
The line #170 with settingsBtn.setAttribute("class", "fa fa-gear"); is no longer necessary and therefore can be removed.
Changing line #169 with const settingsBtn = document.createElement("i"); to some other element type makes the text (and therefore, now the 
emoji) no longer italicized. FYI, I used the following:
const settingsBtn = document.createElement("svg");