Update docs/ global styles,

[panarch]

• Load font-weight: 500.
  500 is properly applied for header and sidebar texts.
  

• Update article h1 styles.
  

• Update h2-h6 styles.
  Update h2 to use Fira Sans font.
  

[coveralls]

Pull Request Test Coverage Report for Build 4794455669

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 7 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.05%) to 98.878%

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Files with Coverage Reduction	New Missed Lines	%
core/src/executor/insert.rs	7	96.34%

Totals
Change from base Build 4777188706:	0.05%
Covered Lines:	42221
Relevant Lines:	42700

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💛 - Coveralls