Any modern browser (i.e. released in 2015 or later) should work: Firefox,
Chrome, Safari, Edge etc. They need to have support for HTML 5, CSS 3 and
Should all the pages here validate as HTML5/CSS?
They should, yes. However, validation services at W3C (http://validator.w3.org/, http://jigsaw.w3.org/css-validator/) are pieces of
software running behind W3C web servers. As such, they change from time to
time and become more strict. On occasion, what validates today won't validate
tomorrow. If you find such pages, let me know.