Update tablet and desktop breakpoints

[domlander]

There are new designs for the Timeline article structure at desktop and tablet breakpoint. This is so that there is some space between the left border line and the left hand side of the page at these breakpoints

Figma designs: https://www.figma.com/file/xPr2tZZger7pszcO075tAQ/New-Formats---April-23?type=design&node-id=4667-8581&mode=design&t=b4qXFuATZmmeZCtq-0

[domlander]

I initially assumed that we should be removing the left and right border lines of the standard article layout, then create our own lines with the timeline element. However, this is not compliant with the Standard article layout so is not something we should like to do. I chatted with Rich and Jamie regarding what we should do and have decided that leaving the bullet point half-off the screen at the exact tablet and desktop breakpoint is a lesser evil than duplicating the left and right border lines - one set for the article layout and one set for the timeline events. Rich also asked that we add some spacing at these breakpoints to add alignment, which is the subject of this new PR