How to style the help text that appears at the top of pages?
What you're looking for is the $messages variable, which is given the following styling by core, yet seems to be removed from that contributed theme:

div.status {
  background-color: #f8fff0;
  border-color: #be7;
  color: #234600;
}
div.warning {
  background-color: #fffce5;
  border-color: #ed5;
  color: #840;
}
div.error {
  background-color: #fef5f1;
  border-color: #ed541d;
  color: #8c2e0b;
}