XF 2.2 Forum Template Background Colour (Between The Banner Image And The Header Tabs)

We've been creating a few different templates for our forum, and an issue we've run into multiple times is that we want the colour of the background to be different for the section between the banner image & the header tabs.

See here, at the blue arrows, for visualization:

Screenshot from 2021-06-25 21-53-25.png

We would like to change this colour, or, make it transparent (such that the banner image would fill these regions).

Our work-around approach thus far has been to chose banner images which blend at the bottom with the background colur for the template (grey-ish in this case). That is not always possible though.

Is there any add-on to help with this? CSS code? Or, a simple setting that we have just missed?
Is that this style? https://xenforo.com/community/resources/ixerius-flat-theme-by-sultantheme-com.8419/

If so, reach out for help with the style author.
It's a modified version of one of the Xderium styles from here:

Normally, Style properties -> Header and navigation -> Navigation row would change that. If it doesn't, reach out to the style author for help.
That did the trick, thank you. Not sure how we missed that before.

The default value for that style/theme was 'fully transparent' (hence having the background colour from below).

So, we can change the colour of it, or, use the banner image (full image), crop it such that the top of the new image seamlessly flows from the bottom of the banner image, and, upload that second banner image.