How does the horizontal scrollbar fit into this flex table when the number of columns becomes very large? Also what about fixed columns and fixed rows and their scrolling?
The whole idea was to avoid a horizontal scrollbar. If the number of columns is too large, I prefer showing them as multiple lines per row rather than let the table overflow the screen horizontally.
About the fixed header rows when scrolling: please see @gregcatalano's comments. If the header row is below some other section, then things do get complicated, you'll have to trap the scroll event. How that's done will depend on whether you're using jQuery or Angular or something else. I managed to get it done in my Angular.js project: I had to bind to the window's scroll event, keep calculating the offset from top, when it reaches 0, add a class to the header to make it fixed. The code is not clean enough to share it here, apologies.