How to Highlight Fields on Rails Validation Errors

Assuming you have an error class for fields in your CSS file:

<% if @user.errors[:name] %>
  <%= f.label :name, :class => "error" %>
<% else %>
  <%= f.label :name %>
<% end %>

Is this what you want?

Extra: here's a section about customizing default ActiveRecord validations CSS.

Edit: (about extra ifs)

# app/helpers/application_helper.rb

def field_class(resource, field_name)
  if resource.errors[field_name]
    return "error".html_safe
  else
    return "".html_safe
  end
end

And then:

# in your view

<%= f.label :name, :class => field_class(@user, :name) %>
<%= f.label :password, :class => field_class(@user, :password) %>
[...]

(I may have make a mistake in there - I'm writing on a phone - but you get the general idea. You can code this in number of ways = infinity, so do it the way you like...)

Rails now have a nice trick up its sleeve..When an error occurs rails put a div with a class .field_with_errors around the error fields. So now you can just target that class and add styling.

To focus on the input you can do

.field_with_errors input{
  border: 1px solid red !important;
}

this css will put a nice red line around the input element while important! will overwrite any existing styles.