How to override values of span tag using a class within a p tag

I have the following code:

<div id="instru_topp">
                <h3>The topping</h3>
                <p><span class="especial">Mix</span> all the -- <span>Ingredients</span>  and pour it on the top cake.
                    After bakin it, you will end up with this:</p>
            </div>

and I want to use the class in the 1ts span tag withing the p tag to override the italics I use with:

#instru_topp p span:last-child {
    text-decoration: underline;
}