XML : changing font-weight for TVML elements

I'm currently working on a TVML app for the Apple TV, and I've been trying to do a few styling adjustments to a few elements.

I've been able to follow the TVML documentation and I've successfully changed the text colour from white to black by doing this:

  <description style="color: rgba(0, 0, 0)">     Selvage banjo authentic messenger bag, pork belly occupy heirloom...etc  </description>    

Now, according to the documentation, I'd like to style it further by changing other styles such as font-weight to light, and font-size.

Here are a few of my attempts in doing so:

1

  <description style="color: rgba(0, 0, 0); font-weight: light">     text goes here  </description>    

2

  <description style="color: rgba(0, 0, 0) font-weight: light">    text goes here  </description>    

3

  <description style="font-weight: light">    text goes here  </description>    

4

  <description font-weight="light">    text goes here  </description>    

I can't figure out how to get it working, unfortunately. I'm using the descriptiveAlertTemplate.