Firstly, please share how you created that slider…I would love to be able to .
Secondly, in terms of changing the alpha color, there isn’t a really sleek way to do so…you could though set conditionals on the element to change the background color and the alpha value

The unfortunate thing is that the alpha value doesn’t accept dynamic data ( something to request as a new feature ), so you are unable to link the alpha value to a value set on the slider.
To change the font size it would be the same thing…conditionals on the text element, which would be a bit less cumbersome to set up than the alpha color because with alpha you’d need essentially 99 conditionals ( unless you use a range value ), but with the text you could determine the number of options to provide.
Other options I believe would be using CSS, HTML or Javascript…none of which I am familiar enough with to instruct on, but I believe in the codes you can use dynamic data, which could be referenced to a custom state or something that stores the value of the slider to set the alpha color or font size in your code.