[CAL-481] improve responsive design for public booking page

[PeerRich]

_{From SyncLinear.com | CAL-481}

[zomars]

We need more context. What is exactly wrong?

[PeerRich]

urgh, talked to @JeroenReumkens when I made this. will follow up with a loom video of the issues

[ciaranha]

I can think of a few issues too

[JeroenReumkens]

@Jaibles I improved responsive also a lot in the new booker. I'll add this issue as a "fixes" issue to the booker PR as well, let's when going through everything together also see if there's more we can and want to improve on responsiveness :)

[JeroenReumkens]

Yesterday we merged #6792 — this improves a lot around responsiveness. There's still some tweaks we're doing, but that makes this issue redundant.