Enable resetting the colour scheme to the system appearance

src/css/exceptions/color-scheme-picker.css

@@ -59,6 +59,12 @@ header > * {
 			}
 		}
 
+		&:has([value="system"]) {
+			&::before {
+				content: "\f390";
+			}
+		}
+
 		&:has(:checked)::before {
 			text-shadow: var(--color-decoration) 1px 0 10px;
 		}