Add two talks by Séb
Add author entity for Séb
Merge pull request #15 from guardian/sc-talks-seb

Add two talks by Séb
Correct image path
Merge remote-tracking branch 'origin/oja-correct-image-path'
Use correct variables
Normalize design
Remove redundant property
Make no assumptions about where heading classes will be applied

Some headings did not have the correct font weight.
Update styling of `alt-h3` to only remove trailing margin
Re-use CSS
Add missing `alt-h3` classes
Add docs on contributing to CSS