Feat: What is the portion between C and X called ?

[kvngvikram]

Requested feature

Is there a way to customise the area between section C and X ?

+-------------------------------------------------+
| A | B | C                             X | Y | Z |
+-------------------------------------------------+

Neither lualine_c nor lualine_x can be used to customise the space between them.

Motivation

I often use vertical splits with two files and when I am focussing on the lower split, I have no clue where the upper split begins. The status line of the upper split should help me here. But the colors are not contrasting enough.

Yes I know its an issue with my theme. I spent lot of time to find the right theme and turns out it doesn't have the right color for inactive splits. And often previews don't show how it will look with split. I just want to select a theme and deal with this split visibility issue later by configuring.

Is there a way to customize it ? If yes, can someone help me how i can do it.

Thank you.