expression, pre-noun adjectival
Pre-noun adjectival used to refer back to a previously mentioned type or situation. Functions like 'such' or 'that kind of' in English.
そうした問題は初めて聞きました。
This is the first time I've heard of such a problem.
そうした理由で、彼は辞職した。
For that kind of reason, he resigned.
こうした points to something near the speaker or about to be mentioned ('this kind of'), whereas そうした points to something already mentioned or associated with the listener ('that kind of').
Derived from the adverb そう (so, like that) combined with the past tense of する (to do), literally 'done like that', functioning as a pre-noun adjectival.