Using Bootstrap framework (version 3.x) on your website? You need to upgrade to Bootstrap 4 or use the PayPal Bootstrap Accessibility Plugin to make the default Bootstrap 3 components accessible for keyboard and screen reader users.
The plugin does not affect the performance or the visual layout of your website.SOURCE]
WEBSITE ACCESSIBILITY TESTING & REMEDIATION SERVICES: Mary Gillen is an experienced Website Accessibility Compliance Auditor and Remediator. She can test your website to determine if it meets accessibility standards:
WCAG 2.1: 312 checkpoints covering A, AA and AAA W3 accessibility guidelines
Section 508: 15 US federal guidelines covered by 59 accessibility checkpoints