Unable to find correct ID for images in image block

I'm attempting to round the corners on my images on two different image blocks. Since Squarespace doesn't seem to natively support rounding corners on images, I was going to do some custom CSS work to round them out. I found this blog entry that gave me the script I needed to enter, but I can't actually properly references the images themselves - only the blocks.

For example, here's a test case I built. I have two image blocks here, both set to the Poster design. This is on one of the default templates without any major changes, save for swapping out some text.

If I hit inspect, the only ID I can find is for the blocks themselves, not the images. I could just be missing it, but this seems to be the only ID that doesn't start with yui (which I was told isn't static and will change every time the page is reloaded). 

If I reference this ID when I try to round my corners, I end up with this - a rounded image block. (I'm also not sure why every time I go into edit mode, the formatting on my test photos I'm using seem to break but that's a whole 'nother thing)

I'm really new to all of this, so it's totally possible I just have the whole thing completely wrong. Anyone got any pointers?

Thanks!

You should share link to check.

27 minutes ago, tuanphan said:

You should share link to check.

https://www.johndunford.com

I'm using those two image blocks at the bottom to test.

3 hours ago, JohnRD said:

https://www.johndunford.com

I'm using those two image blocks at the bottom to test.

Add to Home > Design > Custom CSS

div#page-5dc045bc3ce47a0b8c4fee4a .image-inset {
    border-radius: 50px;
}

That's perfect -it works! How did you find that ID? I don't see it listed there at all.

17 hours ago, tuanphan said:

Add to Home > Design > Custom CSS

div#page-5dc045bc3ce47a0b8c4fee4a .image-inset {
    border-radius: 50px;
}

 

17 hours ago, JohnRD said:

That's perfect -it works! How did you find that ID? I don't see it listed there at all.

 

You need to know html/css....