I used to pull stunts like this all the time as soon as tables came. Really ugly, and may seriously embarrass any validator you run it trough: overlapping table cells. Works in most browsers though and even without css.

No, most css doesn't work in emails, stick to tables and images.

For now though, you're stuck with <table> and CSS2 support for your layouts.

But more so, external style cannot be applied to a subsection of a web page unless they force it into an iframe, which has all sorts of issues of it's own which is why external CSS is usually ignored. Inline CSS is often stripped by the tag strippers who don't want you turning things on or off... and media queries shouldn't even play into it since the layout should be controlled by the page it's being shown inside (for webmail) or the client itself, NOT your mail.

I hate to be the guy who will destroy your day but... Tables. You need to work with nested tables/cells. If you think Gmail is annoying you will cry in agony if you also need Outlook support.Work with the good old HTML from the early 2000's. That's the only way to be sure everything will work as intended.Anything else will mostly result in a horrible mess, broken design and incompatible layouts.

I would try designing your mail-template as "normal" as possible. Tables help a lot for example (yuck).

You'll have to use <table> tags—a method long buried by web developers

While it’s not quite completely table-free, I’ve managed to get The Intermittent Newsletter down to a single table—one that’s not even visible to non-Microsoft email clients. Along the way, I made an effort to make The Intermittent Newsletter accessible to more readers.

How to wrap long word (text without spaces) in html table’s cell? This is very, very easy! We must add only a CSS proprty to table cell “td” tag – “word-break: break-all;” then all column’s widths become as intended. 

It is also very likely that the contents of the table might change the structure or dimensions of the table. For example, long words residing in the table cells can cause the cell width to increases. If you fix that problem, it might happen that the long words cross the cell boundaries.