optimize accessibility

[alessandromenini]

General

https://developers.google.com/web/fundamentals/accessibility/

Forms

https://www.nngroup.com/articles/errors-forms-design-guidelines/

Tabs

• Add tablist role to the <ul> to indicate it contains tabs.
• Add presentation role to each <li> to bypass its list item state.
• Add tab role to each <a> to incidate it is an actual tab.
• Add href and aria-controls to each <a> to reference its tab panel.
• Add id to each <a> as a reference for its tab panel.
• Add aria-selected="true" to the active <a> tab.
• Add tabpanel role to each <section> to indicate it is a tab panel.
• Add id to each <section> as a reference for its tab.
• Add aria-labelledby to each <section> to reference its label.
• Add hidden to each inactive <section> to indicate it is hidden.

https://gist.github.com/jonathantneal/435478e415bfe4f54d06