Proxima Nova (fonts.com). Semibold, regular & thin variants:
font-family: "Proxima N W01 Smbd", "Proxima Nova Semibold", 'Helvetica Neue', Arial, Helvetica, sans-serif;
font-family: "Proxima N W01 Reg", "Proxima Nova Regular", 'Helvetica Neue', Arial, Helvetica, sans-serif;
font-family: "Proxima N W01 Thin Reg", "Proxima Nova Thin", 'Helvetica Neue', Arial, Helvetica, sans-serif;
Brawler (Google fonts). One variant:
font-family: 'Brawler', serif;
<link href="https://fonts.googleapis.com/css?family=Brawler" rel="stylesheet">
Based on the Perfect Fourth scale.
Base font style is html { font-size: 62.5%; }
meaning that 1 rem = 10px. Default line-height is 1.5.
Note: The API docs are an exception, with a base font of 1.6rem / 16px.
Paragraph text. Proxima Nova Thin, 2rem / 20px, line-height 1.5
Small text. Proxima Nova Thin, 1.4rem / 14px, line-height 1.5