#18: layout fixes

assets/scss/_variables_project.scss

content/ja/docs/accounts/_index.md

content/ja/docs/audio/_index.md

content/ja/docs/collections/_index.md

content/ja/docs/donations/_index.md

content/ja/docs/labels/_index.md

content/ja/docs/plugin/_index.md

content/ja/docs/prayers/_index.md

content/ja/docs/quickstart/_index.md

content/ja/docs/steps/_index.md

content/ja/docs/study/_index.md

content/ja/docs/verses/_index.md