Change default picture size

I’d like to change the default size of the picture from 150px x 150px to 275px x 350px.

I changed the size in Chrome Inspector by adding the CSS below, but when I view the rotator page, the changes don’t reflect.

.testimonial_rotator_img {
width: 100%;
max-width: 275px;
height: 350px;
}

I tried adding this to CSS, but it didn’t work either:

.testimonial_rotator_single.has-image.template-default {
width: 100%;
max-width: 275px;
height: 350px;
}

But the CSS I added to change the color of the stars has remained throughout both the single and rotator view:

.testimonial_rotator_star {
color: #ff551d
}

Any ideas how I can change the image to a new default size of 275 x 350?

The page I need help with: [log in to see the link]