CSS Linter results.

[tansiret]

	line	column	title	description	browser
	5	1	Parsing Errors	Unknown @ rule: @define-color.@define-color theme_fg_color rgba(255,255,255,0.96);	All
	81	33	Parsing Errors	Expected RBRACE at line 81, col 33. -gtk-icon-transform: rotate(1turn); } }	All
	1281	33	Parsing Errors	Expected RBRACE at line 1281, col 33. -gtk-icon-transform: rotate(1turn); } }	All
	5909	19	Parsing Errors	Expected RBRACE at line 5909, col 19. background-color: #F04A50;	All
	5937	19	Parsing Errors	Expected RBRACE at line 5937, col 19. background-color: #F04A50;	All
	5951	19	Parsing Errors	Expected RBRACE at line 5951, col 19. background-color: #F04A50;	All
	5965	19	Parsing Errors	Expected RBRACE at line 5965, col 19. background-color: #F04A50;	All
	6899	8	Parsing Errors	Expected COLON at line 6899, col 8.infobar.error button.sidebar-button,	All
	9615	31	Parsing Errors	Expected RBRACE at line 9615, col 31. -gtk-icon-transform: rotate(0turn); }	All
	9620	32	Parsing Errors	Expected RBRACE at line 9620, col 32. -gtk-icon-transform: rotate(-0.5turn); }	All

0 lines 10 errors 2728 warnings

[tansiret]

Stupid results. Theme is working fine, fine.

[mkg20001]

Did you set the correct parser? Possibly gtk allows special CSS-things.

Try stylelint --fix file to auto fix