Use colors to convey the meaning of values in the calltree

[julienw]

In the [hotspot tool](https://github.com/KDAB/hotspot], the values are also displayed using a colored background. The colored background itself had a width that depends on the value. This is nice because this stays accessible: the absolute value are still displayed, and the color isn't the only thing that conveys the meaning, as the width changes too.

┆Issue is synchronized with this Jira Task

[gregtatum]

I believe Victoria's mockups had something similar, but not color coded:

[zoepage]

I love how they mockups do it. Could also work with a thicker colour coded border, with expanding to a square on hover / focus.