The pattern is my well-loved Butterick 3344 and I made this same version in white earlier this summer. I didn't like the bias-cut of the white one and the back facing keeps flipping out, so I changed both of those things. There is plenty of stretch with it cut on the straight grain rather than the bias. The back of the neck opening is finished with bias tape. The arm holes are finished the same way.
This fabric has been in my stash for a few years. I purchased it as a remnant, so there wasn't much of it to work with. I'm not sure what the fiber content is, but it is a jersey and the stripes are created with a burn-out pattern.
I underlined the brown fabric with an ivory knit fabric that I'm also unsure of the fiber content, but it was also a remnant about the same size.
It seems this was the summer of the sleeveless top for me. I made six if I include the running top. Perhaps that is too many and puts me into the "stuck in a rut" category, but I think sleeveless tops are flattering, they work well under cardigans (hate that sleeve bunching) and I have a hard time finding short sleeves that I like. I feel silly in puffed sleeves and flutter sleeves have never appealed to me. The length of a short sleeve needs to be just right to be flattering. I've been burned by this before. Lately I've been admiring sleeves that end just above the elbow. That might be worth a try for me.