codeigniter 2.x.x validation error highlighting

where/what file to tweak in order to alter the background color of the form_validation error ? , like e.g I want to change the color to red, so that it stands out on my registration form, when it detects an erro开发者_如何学JAVAr when user enters inappropriate data

First you should mark the errors, changing the error default delimiters:

$this->form_validation->set_error_delimiters('<div class="error">', '</div>');

and then style the error class in your css, like

.error {
    background:#FBE6F2 none repeat scroll 0 0;
    border:1px solid #D893A1;
    color:#333333;
    margin:10px 0 5px;
    padding:10px;
}

check into the documentation here