Improve css for blog posts

Fixes #652 (closed)

To be approved!

Improvement on blog posts styles

• Paragraphs and list items<li> : justified
• Blockquotes: font-size was bigger than <p> => now:
  • Font-size: equals to <p>
  • Color: lighter than <p>
  • Font-style: italic
• Notes: were the same size as <p> and looked exactly like blockquotes => now:
  • Font-size: 10% smaller than <p>
  • Font-style: italic
  • Color: lighter than <p>
• H3 <h3> headings: were too close to <h2> => now:
  • Padding-top: leaves more space between h3 and the h2 immediately above it

How to apply notes styles

**Note:** Lorem ipsum dolor sit amet, consectetur adipisicing elit. Amet sit repellat facilis inventore necessitatibus, doloribus laboriosam tempore error deleniti? Minus, esse vitae voluptate commodi debitis! Libero hic quam sunt, a.
{: .note}

{: .note} does the tricky part: adding a class .note for the paragraph immediately above it. Must not exist a blank line between the paragraph and the markup to add the class.

Results:

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cc/ @axil