Reading Mode caps the body text of chosen content types at 45rem so lines stay short enough to read comfortably, while the rest of the page keeps its full width.
Why a line-length limit
A comfortable measure is roughly 60 to 75 characters per line. Past that, the eye loses its place on the return sweep and long articles feel like work. On a 1600px layout an unconstrained paragraph can run well over 150 characters, which is why long-form pages on wide themes feel harder to read than they look.
Switching it on
The setting is called Reading Mode (45rem/720px) and lives on the Typography & Content tab of Global Site Settings. It is a multiple-select of your content types, not a checkbox — hold Ctrl or Cmd to pick several. Select Article and Basic page, leave landing pages and product types out, and save.
Exactly what it constrains
Solo adds a reading-mode class to the node, and the stylesheet narrows only the long-text fields that are direct children of the node content in the full view mode: the plain long-text field and the long-text-with-summary field. Everything else is untouched. That means:
- Teasers and listings are unaffected — the rule targets the full view mode only.
- Images, embedded video, tables and views placed inside the same node keep the full content width.
- Fields rendered through a custom display or a paragraph are not direct children of the node content, so they will not be narrowed.
The constrained field is also centred within the content region, so the page does not look lopsided when a sidebar is absent.
Try it on one type first
Pick your longest-form content type, switch it on, and compare a real article before and after on a desktop screen. If you use different display settings per content type, customising node edit forms per content type in Solo covers the same per-type thinking. Solo supports Drupal 10.1 through 12; the theme is on the Solo theme page.
Prefer a sub-theme configured properly the first time? That is Drupal theming — or get in touch and describe the site.
