How to make thumbnails overlap the slider image in a gallery section

I added a gallery section in my 7.1 website and I set it to "simple slideshow" with thumbnail feature. Now I want to make the thumbnail to overlap the slider image. I have included my present gallery section and the result I want to achieve in the images below. Kindly check them out. I'll be glad if you can provide a solution.

Hi,

I think we can use some CSS negative margin to move up thumbnails 

Can you share link to page where you added gallery? We can check easier

We can use CSS code like this to make thumbnails overlap slider image

section[data-section-id="66b387fcef19ee1c529fd9dd"] .gallery-slideshow-thumbnails {
  position: absolute;
  bottom: 50px;
  right: 0;
}

Note:

section[data-section-id="66b387fcef19ee1c529fd9dd"] is Gallery Slideshow ID. Replace with your ID.