Forgive me. I am not an expert at CSS/HTML.
I noticed if I have an error in the woocommerce cart, such as adding more product while in the cart then what is in stock, the output is a UL list at the top of the page. Unfortunately, it does not show up stylized and so the error message is not noticeable by the customer as it looks like the regular text on the page. I am not sure if it was a style choice by design or an error on my part but I had two complaints because they did not notice they were doing something wrong when they kept on trying to edit their cart.
I cut, copied and pasted the below to make it stand out to customers. It is ugly and, if you have more than one error at a time I am not sure what the output will look like but it gets the job done.
/**Woo Error Message **/
border:1px solid #941210;
margin:0px 0px 23px 0px;
padding:10px 10px 10px 32px;
Anyone else done something better feel free to post and share. =D