That's correct. In negative sentences using the partitive, de is to be used -> Les chiens me mangent pas de chocolate. https://grammar.collinsdictionary.com/amp/french-easy-learning/the-partitive-article-du-de-la-de-l-and-des
That's not quite right.
"De" simply means "of". It is not a variation of the definite article.
"Les chiens ne mangent pas du chocolat", where "du" is the merger of "de" and "le" in French. Literally "The dogs do not eat of the chocolate". Generally "du/de la/des" (de + les) is the partitive, roughly comparable to the English "some" but not used in all the same contexts.
"The dogs can not eat chocolate" would be "i cani non possono mangiare il cioccolato."
English uses the auxiliary "do" when we want to emphasize something (I do eat chocolate), negate something (I do not eat chocolate), or ask a question (Do I eat chocolate?). In Italian, they just negate the verb directly: non mangiano, literally "not eat." To say "can not eat" involves bringing in an entirely different verb, one that means "is able to," and then negating that.
While that is all technically correct, in English the meaning behind the phrase is the same. "Dogs do not eat chocolate" = "Dogs cannot eat chocolate". At least to dog lovers/dog owners it is. So if I were translating this from Italian in some pet journal, I'd translate it either way depending on the context.
"Dogs cannot eat chocolate because it..."
"Dogs do not eat chocolate because it..."
would be the same context.
That's irrelevant. Duolingo is teaching us vocabulary and grammar/syntax. That's it. We're given single sentences at a time, sometimes just noun phrases. Gleaning greater meaning from those, where there just is no context to inform a broader interpretation, is a bad idea.
Even in your previous comment, where you equated "do not" with "can not," you were also implicitly equating "can not" with "ought not," and all three are very different concepts. I do not swim. It's just not an activity I participate in. I have the ability, and there's no reason why I shouldn't. I just don't. I can not speak Chinese. I never learned how. There's no reason why I shouldn't, it's just not something I pursued, and if I were to attempt to do so right now, I would fail miserably. Dogs ought not eat chocolate. They most certainly can, and occasionally they do, and that's how we know it's bad for them.
This is exactly why, for now, within Duolingo, we should stick to translating and not try to dig deeper. Duo's not giving us animal safety lessons. So it gave us "Dogs do not eat chocolate." So what? It also gave us "The monkey reads a book." There's no commentary being delivered there, just a sentence to be transformed into its closest English equivalent.
I'm not saying it can't ever be done. I'm saying it shouldn't be done here or now. I keep coming back to a lack of context to inform an interpretation. A body of work can be interpreted. A single sentence must only be translated, because anything more is making unwarranted assumptions.
If I recall, this sentence was an Italian to English translation, and English has its allowances for utilitarian purposes when translating from their "foreign" languages. By implying that this can't be done in the languages we're trying to learn and it's to be adhered to <sub>strictly</sub> to grammar and syntax then we're never going to learn the language for its broad utilitarian purpose.
Why <sub>shouldn't</sub> it be done here? Some of us are here to learn a language different from our own native tongue, for our own purposes. If we can learn that there's really no difference when you leave out the "io", we should be able to learn other things too. But fair enough, your argument. A bit strict, but fair in its own right.
Here is quite an extensive explanation about the Italian definite articles:
Well of course it depends on what type of chocolate and how much theobromide it contains in relation to the size of the dog and the dog's general health. White chocolate is pretty safe, at least more than any dark chocolate. BTW, I'm a veterinary technician. Your dog must not have ingested enough to make him sick, thank goodness for that. But chocolate is still bad for dogs because their liver does not metabolize it in the same way that a human's does.
No one here has the ability to deal with technical issues. Next time something like that happens, try rotating your screen to see if more tiles populate the word bank. You can also take a screenshot and file a bug report: