Use the %form_errors_message% along with a keyword modifier to put a class on the <div> wrapping the errors. So for example <div class="%form_errors_message^notempty:show-errors^empty:hide-this-div%"
Use the tagif modifier on the form errors keyword to add a tag to it and style that with CSS instead of the outer wrapper, for example: <div class="errors">%form_errors^tagif:div%</div>
Try any of those and let us know if that works/helps.