Thanks for flagging the image issue, I think there's an issue with the responsive image serving code that doesn't work consistently across browser. Temporarily disabling that for now & pushing a new update.
Also, you are right about using \mathrm{d}x. Another friend also just flagged it to me as well, I will update the post regarding this!
Also, you are right about using \mathrm{d}x. Another friend also just flagged it to me as well, I will update the post regarding this!