fix broken website on small screens

[lictex]

#302

sidebar & navbar are collapsed into the hamburger menu

side effects / fixes note:

• backdrop blurs now work in dark mode
• code blocks will scroll instead of wrapping if overflowed
• sidebar is pinned on desktop screen
• slightly increased blur radius for better text readability
• main text's max width is limited to around 900px
• slightly reduced the font size of sidebar
• added a small margin on index page

[codecov-commenter]

Codecov Report

Merging #331 (99542dd) into master (619c300) will decrease coverage by 0.10%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #331      +/-   ##
==========================================
- Coverage   73.15%   73.04%   -0.11%     
==========================================
  Files          40       40              
  Lines        5435     5443       +8     
==========================================
  Hits         3976     3976              
- Misses       1459     1467       +8     

Impacted Files	Coverage Δ
website/src/main.rs	0.76% <0.00%> (-0.05%)	⬇️

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[lukechu10]

Seems like I'll need to bump MSRV because of bumpalo. Thanks for the contribution!