What is even is "marriage" in the quran?

I made post last time about pre-marital ideas in the quran not existing and someone said something like this:

sex before a legal marriage or sex before a quranic marriage? The former is not haram. the latter is haram

What is Quranic "marriage"? And how is it different from so called legal one? What's the criteria?

The criteria for so called "islamic" marriage does not exist in the quran, ideas like mahr/dowery, wali and witnesses does not exist in the quran it call came from fiqh books.