Slightly narrower layout with a few margin changes

[taiyab]

A few modifications to the homepage layout.

Namely:

• Making it slightly narrower
• Modifying margins and spacing slightly
• Changing the position of the code graph illustration

Feel free to completely veto @traceyljohnson, this is your thing.

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[taiyab]

@traceyljohnson @chris-sev Bump.

[chris-sev]

@taiyab sorry for the delay. merged! thanks!