chrome/browser/resources/extensions_infobar_mac.css

/**
 * The following style rules affect Extension Infobars on the Mac.
 */

body {
  background: -webkit-linear-gradient(#EBEBEB, #CFCFCF);
  font-family: 'Lucida Grande', Helvetica, sans-serif;
  font-size: 12px;
  height: 36px; /* Infobars are limited to 36-72px */
  margin: 0 38px;
  overflow: hidden;
}