SQL in a sidebar - Milestone 2: Visual tweaks (#40694)

* Move all notebook containers styles to one place

* Make NotebookStep wide again

* Tweak sidebar width and breakpoints

* Remove top margin from NotebookSteps

* Stop line wrapping in an ace editor

* Uniform width between step header and step body

* Remove stray styles

* Scroll content independently

* Use named export

* Use Mantine button for "Visualize"

* Convert notebook step width to rem

* Adjust the position of the step close button

* Adjust notebook step max-width to 1200px

* Remove the `cx` where not needed

* Use HTML 5 `aside` element for the sidebar

* Use Mantine responsive styles

* Fix E2E test