elementCss static method
Build CSS for an html element.
selector is the element selector, like body or h1. You can chain selectors
like body h1 or body, h1, etc.
properties is a map of CSS properties and values, like color: #000000;.
Example of string built:
CssBuilder.elementCss(
 selector: '.note-editable',
  properties: {
  'color': '#000000',
  'background-color': '#ffffff',
  }
);
Result:
.note-editable {
 color: #000000;
 background-color: #ffffff;
}
Implementation
static String elementCss({required String selector, required Map<String, String> properties}) {
  var css = '$selector{';
  for (final entry in properties.entries) {
    css += '${entry.key}:${entry.value};';
  }
  css += '}';
  return css;
}