Navigation top bar causes horizonal overflow

Problem/Motivation

The navigation top bar displays the current page and that pages actions (edit, delete, etc). As such, the content of the topbar needs to be taken into account when styling. In the current release of Drupal core, when viewed on narrower screen widths, the top bar can overflow the width of the viewport causing whole-page horizontal scrolling.

Steps to reproduce

1. Install drupal core with the standard profile
2. Enable the navigation module
3. Create a new basic page with a long-ish title
4. Shrink the viewport down & observe the overflow

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet