rootStyleToCss function
Converts a style map into root-level CSS declarations.
Implementation
String rootStyleToCss(Map<String, Object?> style) {
return style.entries
.where((entry) => entry.value != null && entry.key != '_cssText')
.map((entry) => '${entry.key}: ${_rootCssValue(entry.key, entry.value)}')
.join('; ');
}