70s Rainbow Striped Seersucker Maxi Sun Dress by At Home Wear Sears size S??

Vintage 1970s rainbow striped seersucker sun dress. Approximate measurements while lying flat: 53” long, busy 14.5”, and waist 20”. Button up from waist, front zipper, unlined. In good condition, I did not find any issues. No size tag, but my guess is an XS or S. Please go by measurements.