Extension attempts to add class before `#board` is loaded

[sxxov]

Error handling response: TypeError: Cannot read properties of null (reading 'classList')
    at chrome-extension://aldklnbenbdgfgfbflalmlddkkndgnlc/js/init.js:6:13

that line specifically is:

board.classList.add(result.classList);

[sxxov]

it would seem that i have an old version of the extension from the chrome webstore (before #54 was merged). however it doesn't seem like that PR would fix this issue. my hunch would be the callback for chrome.storage.sync.get fires earlier now than before.