CSS code to change image size in AJAX results

Hello,

I need to have my featured images in AJAX results to all have the same size. Preferably, thumbnail size. Can someone help me with the CSS code?

I have this code so far:

img {
border: 1px solid #ddd; /* Gray border */
border-radius: 4px; /* Rounded border */
padding: 5px; /* Some padding */
width: 150px; /* Set a small width */
}

However, the images still come out in different sizes.