Civic Accessibility Toolbar provides a block with accessibility utilities to help users change colour contrast and font size.
The module allows you to create a block with both or one of the utilities to help visual impaired users accessing your Drupal site.

All theme font sizes must use rem or em units, for the font resize utility to work as expected.

The module is tested with Bartik, Garland, Zen Starterkit, Stark, Oliveiro themes.