Copy old style.css code into /styles/legacy.css file
Start new styles in style.css: section 1 - reset
new styles: section 2 - repeatable patterns
new styles: section 4 - header and navigation
new styles: section 5.0-5.5 entry header, entry meta, entry content, galleries
new styles: add section 5.7-5.8 attachments and post/paging navigation
new styles: up to section 5.13 - comments
new styles: section 6.0 widgets and asides
new styles: section 7.0 footer
new styles: add placeholder sections for 8.0-9.0 medua queries and print styles
Replace #content with .site-content
Replace #primary with .primary-aside
Correctly target .widgettitle in asides instead of heading level