How to Add Css Image Pulsating Code

[cyber]

1. I want to add an image and a css code that makes image pulsate. How do I add it? The shopify theme.css file is a little difficult.

2. Also I want to add a video background image with using an app that cause video to load slowly. I Uploaded the video and tried adding it to theme.css via the body class ".template-index {background-image: url("https://cdn.shopify.com/s/files/1/0536/3436/7679/files/smoke_bQpOtfpV.mp4?v=1611344599");
}" but its not loading. What am I doing wrong?

[KetanKumar]

@cyber 

Sorry for facing this issue, it's my pleasure to help us.

Welcome to the Shopify community!
and Thanks for your Good question.

Please share your site URL,
So I will check and provide a solution here.