WordPress has many accessible ready themes created by developers which you can use for your OER.
The WordPress community and the open source WordPress project is committed to being as inclusive and accessible as possible. We want users, regardless of device or ability, to be able to publish content and maintain a website or application built with WordPress.WordPress aims to make the WordPress Admin and bundled themes fully WCAG 2.0 AA compliant where possible.
Finding accessible-ready WordPress.Org themes
Accessibility on the web can mean a lot of things. But in general it means making websites as inclusive to as many users as possible. Accessibility is important for a diverse group of users including mobile users, people who rely on assistive technology to navigate the web, and even search engine robots.
Finding accessible-ready WordPress.COM themes
To search for an accessible-ready theme for a WordPress.COM site