How to find out more about theming bonuses in-game?

I found theming bonuses often referenced in strategy guides and discussions. But I couldn't find it in Civilopedia or when hovering over wonders/buildings. How can I find it? I have BNW

Go to the Culture Overview screen, to the tab that displays where all your Great Works are housed.

In buildings and wonders that have more than one slot for a Great Work (e.g., any Museum, the Great Library, the Louvre, etc.) you will see a +0 next to the great works in that building. If you mouse hover over that +0 it will tell you what you need to do to earn the theming bonus from that building/wonder. It may tell you that you need, for example, 2 great works of writing from different eras and different civilizations. If that building has two Renaissance writings from your civilization, you can go the trade screen (the next screen in the Culture Overview) and see if you can trade one of your Renaissance writings for, e.g., a Medieval writing from another civ. If you can do that trade, you will see the +0 theming bonus turn into a +2 (earning you both +2 tourism and +2 culture). Rinse and repeat for other buildings and wonders.

if you can't do a trade, you can always go on the warpath and conquer cities for more great works. (Note that the AI is usually smart enough to evacuate as many Great Works as it can before the city falls, which places a premium on taking a great works-rich city in a single turn.)

Finally, when you bulb GWAMs to form great works should be informed by your needed theming bonuses. For example, let's say you are in the Renaissance Era and have a 2-slot building that has one empty slot and another that has one of your Renaissance Works of Art and the theming bonus tooltip tells you that you need another Work of Art from your civ, but from a different era. If you have a spare Great Artist sitting around, consider saving him until you enter the Industrial Era -- when you enter Industrial, bulb the GA for a new Great Work of Art and put it in the empty slot -- instant theming bonus. But if you were impatient and bulbed the Great Artist while you were still in the Renaissance Era, no theming bonus.

Nuggets like this, are why I read Civfanatics regulary; to up my Game !

I will say that the best theming bonus is the internet.