Merging cells inside columns

I am using “tanstack/react-table” v8 and my table is quite nested and sort of complicated. What I want is a expandable rows, with dynamic cell content, like a accordion. Somewhat like the one in the picture. I got the expandable logic working but I can’t find a way to style my column like that. How can I achieve such styling I tried merging cell but I couldn’t. Any help ?