getElementByClass?

getElementByClass?

Hi everyone!

To start, I know nothing about js so be gentle.
I'm designing a blog and I want each post on the page to be in it's own cloud. So I have a top image, a repeating slice for the middle and a bottom cap. All of these elements fit together very nicely if the entire middle image is used but because the middle section's height is different depending on the content it doesn't line up with the bottom cap.

Cutting to the chase, I need a way to specify the height of multiple divs based on class name to be rounded-up to a multiple of the height of the repeating middle image. I found a way to do this for a div based on ID but there will be multiple instances per page. It looks like Jquerry can do something with getElementByClass but I don't know how to implement it.

Thanks for any advice!