I investigated this issue and it seems that it would be difficult to change this style. Inspecting in DevTools and changing the text property, the text disappears!
My hope was to change the style defined in the file layout.js.
As workaround, I had to create and apply a new Layout to my page. This layout has a custom header (with a Text defined as center/bold/heading6) on top of a ScrollContainer, as shown in the image below:
Maybe trying a little more on layout.js would be possible to get the desired result, but it seems weird to me the fact that the text dissapears when we change its property on DevTools…
Anyway, I hope this helps!