input-widget: slider: value preview can go off the screen

[ES-Alexander]

Bug description

Steps to reproduce

1. Add a slider to the top-bar
2. Move it
3. The value indicator is clipped off the top

Primary pain point(s)

It looks unpolished, and makes it hard to tell what value you're on.

Additional context

Discovered while testing v1.16.0-beta.13

Prerequisites

• [x] I have checked to make sure that a similar request has not already been filed or fixed.