How to align in an editable text field, the text at the top ???

Good morning everyone,
I have a problem that is driving me crazy. I am designing a web page in Axure RP 8 where I have to simulate a text field where a description can be entered. I insert the text field on the page and so far so good. The problem that is created is that I cannot vertically align the text at the top (it gets stuck in the center). I saw there are buttons to do this but when I select the text field, they become inactive. And when I deselect it they are activated but clicking on them nothing happens.

Can you help me?

Even with a sample file or a small video.

Thank you in advance

Maria