If you use client-side-validation in CActiveForm it assigns the class "errorCssClass" to the element wrapping <label> and <input>. If you disable JavaScript and you submit the form the class "errorCss" will be assigned directly to <input> and <label>, so that you have to write your CSS two times, usually it should be no problem to unify the assigning of the class, either both to the element wrapping or both directly to the elements.
Example:
JS validation:
<div class="ym-fbox-text ym-error"> <!-- here the errorCssClass -->
<label for="ContactForm_email">E-Mail</label>
<input type="text" id="ContactForm_email" name=
"ContactForm[email]">
<div style="" id="ContactForm_email_em_" class="errorMessage">
E-Mail may not be empty.
</div>
</div>
JS disabled:
<div class="ym-fbox-text">
<label for="ContactForm_email" class="ym-error">E-Mail</label><!-- here the errorCss -->
<input type="text" class="ym-error" value="" id=
"ContactForm_email" name="ContactForm[email]"><!-- here the errorCss -->
<div id="ContactForm_email_em_" class="errorMessage">
E-Mail may not be empty.
</div>
</div>