On *rem* support in modern and old browsers.
--
html { font-size: 62.5%; }
body { font-size: 14px; font-size: 1.4rem; } /* =14px */
h1 { font-size: 24px; font-size: 2.4rem; } /* =24px */

Pixels - a fall-back for old browsers like IE6-8, Opera (less than 11.10).