Image Sizes

I recently asked how to make the image sizes for single listings smaller and appreciate your response:

For the image of single listing page, please add the following code.

.bSeCont #directorist .atbd_listing_details .single_image img {
width: 50%;
}
.bSeCont #directorist .atbd_listing_details .single_image{
text-align: center;
}

Can you tell me where to add the code?

Thanks again…