Can anyone guess the mistake I made here?
If you said the html attribute, you're correct. I unconsciously wrote
class instead of
style! It may seem obvious to you but it wasn't immediately obvious to me. I kept looking through the actual content inside the single quotes for errors before finally looking at another HTML email and comparing it to mine. That's when I realized that I typed "class" instead of "style". This a friendly reminder to all you class enthusiast that email markup uses the style tag, no matter how weird it is to type.