[WebDev WaxLotus LLC]

Until someone who know what they’re doing chimes in… you could use CSS Selectors (of your own making e.g. ‘foo’) to trap and apply styles to elements with the ‘foo’ attribute…

[foo]        -- Has an attribute named "foo"

[foo="bar"]  -- Has an attribute named "foo" with a value of "bar" ("bar")

[foo~="bar"] -- Value has the word "bar" in it somewhere ("blue bar stools")

[foo^="bar"] -- Value begins with "bar" ("barstool")

[foo$="bar"] -- Value ends with "bar" ("I was at the bar")

[foo*="bar"] -- Value has bar somewhere ("I was looking for barstools")

So I guess, if you had <img foo='inpost'... and

[foo ="inpost"] { background-color: transparent; max-width:100%;} that might work.

If you posted an actual link to the test site (or emailed it), folks could use FF web developer plugins etc to nail down the CSS tree for that theme…

I hope this helps.