docs: fix mixed indentation for css files

.editorconfig

@@ -15,6 +15,8 @@ indent_size = 4
 indent_style = unset
 indent_size = unset
 
+[*.css]
+
 [*.dia]
 indent_style = space
 indent_size = 2

docs/_static/css/custom.css

 /*
-  This fixes the vertical position of list markers when the first
-  element in the <li> is a <pre> block
+	This fixes the vertical position of list markers when the first
+	element in the <li> is a <pre> block
 
-  Scrolling inside the <pre> block is still working as expected
+	Scrolling inside the <pre> block is still working as expected
 */
 .rst-content pre.literal-block,
 .rst-content div[class^='highlight'] pre {