feat: Warning icons on colors that are used by adw-gtk3

[lassekongo83]

Feature description

Some color values that are used in adw-gtk3 have an icon that says it's not supported.

The following color values are in fact used by adw-gtk3:
@headerbar_shade_color (Used for the headerbar bottom border.)
@card_shade_color (Used on lists.)
@dialog_bg_color
@dialog_fg_color

It would be nice if these could be updated.

Gradience version: 0.4.1 flatpak

Additional Context

No response

Did you read the Code of Conduct?

• I have read the Code of Conduct.

[github-actions]

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[tfuxu]

Updated in commit 905b314. Thanks for reporting