What is the abbreviation of btn in Love between Light and Night?

as follows:

1.btn is actually the abbreviation of English button, which means button in Chinese.

2. Of course, if most players have poor English vocabulary or give corresponding hints.

3. I don't know it thoroughly, so it's really difficult to guess such a word.

Game background

A rising star designer in the fashion world is passionate and pursues shining dreams. As everyone knows, the trajectory of fate has quietly opened.

Light and night are the romantic overture written in the vast Millennium, and the last motto of exiles.

and our story, after all, is the meeting of reincarnation?

Move the pointer of choice, open the unknown fog and point to your own future.