Also, you should make your thread title a wee bit more descriptive as well as describe better what you want. Just posting an image with an arrow is not enough. Do you want the triangle, the bottom toggle slider for that element? Are you asking how to place an element within another element. With a better description I could be answering your actual question right now instead of guessing what your question is.
I'm assuming the post , but do not know if he's wanting to
A) Collapse the whole thread
B) Hide that specific post
The link he is pointing at is not an XF site, it's a Wordpress site and that arrow moves the descriptor box of the designer (apparently a wedding designer - gown or what I didn't read) downward and then upward.