The line-height of the paragraphs goes from 140% to 180% between two breakpoints (320px and 960px). If the default font-size was changed, the bigger line-height ratio will change slightly as well, but remain reasonable.
(The smaller gray numbers are the actual line-height as a ratio, computed with JS.)
Bigger text — Lorem ipsum dolor sit amet, consectetur adipisicing elit. Aut consequuntur distinctio enim iure nesciunt officia quia saepe veritatis? Ab aliquid dolor iste mollitia provident soluta voluptas? Distinctio dolore tempore tenetur!
Ab aliquam at blanditiis cum delectus eaque ex fuga, fugit hic, illo impedit laborum natus nesciunt nisi nostrum placeat ratione rerum sequi similique sit? A corporis debitis delectus deserunt ea eos harum libero maiores necessitatibus nemo nobis odio omnis, placeat quasi, rerum sunt voluptatem! Dignissimos enim, facilis illo itaque nemo tempore. Adipisci, eos, illum.