The column gap of the new sections layout shouldn’t be only changeable through the yaml of a theme.
Please transfer it to the view-settings of a tab with sections-layout.
Alternatively transfer it to the yaml of this view.
Advantage: the column-gap can be changed on standard theme which I would expect as normal.
I agree, and this becomes more of a problem when using sections that span multiple widths. Take for example, my home view, which has three sections of width=1, and 1 section of width=3:
So it’s not only the gap between sections but gap between cards within a section as well.
This particular CSS variable is merely an average CSS theme variable.
All CSS theme variables may be changed in a custom theme.
Why this particular variable should be an exception.
Because there is no better way to control section spacing, yet.
I would not expect this kind of config being configurable from the theme at all.
This should be a configuration for the section view with some system wide default overridable per dashboard in it’s settigs.
Why is this even in the CSS? Doesn’t make much sense to me honestly🤷♂️
Off-course choosing much less wasteful default spacing would reduce the need to modify this in the first place 
Any web page in HA is created using css. For some css properties like font-size, particular color or spacing their values are not just hardcoded - they may use so called css theme variables.
Some of these variables have default values hardcoded, some are not defined at all; in both cases a user may either override a particular variable in a custom theme or define this variable “1st time” in a custom theme.
I have nothing against the ability to override graphical appearance by the theme. It’s always nice to give the user the option to customize the look and feel to it’s heart content.
I would just expect the theme to be the way how to change colors and fonts and not object positioning on the page🤷♂️ If the theming is so powerful it can do even that, good, but it shouldn’t be the primary way of doing that.
To change the placement of sections on the page I would expect config options in the sections settings. If not for other reasons than because if you already use custom themes for different devices/users you want the sections spacing to remain the same no matter which theme you use.
Also not everyone wants to override default HA theme.
