Change border color of '.article-header' and '.blog-footer'
Add 'source/stylesheets/_variables.scss' and its import directive
Define '$article-body__heading--first-level'
Move style definition for '.article' into 'source/stylesheets/_blog.css.scss'
Add 'source/stylesheets/_placeholders.scss' and its import directive
Move placeholder selectors into 'source/stylesheets/_placeholders.css.scss'
Rename module in '.blog-aside' from 'archive' to 'nav'
Rename placeholder selector from '%date-published-sub' to '%date-published--sub'
Unnest '.article-meta'