Testimonials grid section using Grid

Odd, but this Junior level challenge was easier than previous newbie ones, but nevertheless I had some parts where I stuck for a while.

1. Background image (bg-pattern-quotation.svg) positioning was a little bit tricky and I am still not sure that I have done it right. Its centre is positioned at 75% from the left of container and I havent found easy way to repeat it. How to position background image exactly as it is done in the challenge designs?
2. I used <article> and <header> tags for HTML markup. Is it valid use of this tags ?

Will be glad to receive any feedback.