yiisoft/yii2 — pull request #1647 by andy5 (2013-12-27 04:50:29+00:00)
Title: Change ActiveField.hintOptions

Twitter Bootstrap has the "help-block" class for hint text: http://getbootstrap.com/css/#forms-help-text

There is no "hint-block" class and thus hint text doesn't look pretty. Another option could be to add custom style for "hint-block" class into site.css.