use grid instead of flexbox, s.t. we can align the whole timeline left or right

[HannesGitH]

aligning the whole timeline to the left is currently (afaik) only possible by setting the left items to flex:unset and making sure they all have the same length.

if the package would use grid layout under the hood that could be done automatically

[K-Sato1995]

@HannesGitH

Hi! Thanks for creating an issue!
Great idea! I'd love to make that change in my free time.
PRs are always welcome too!