Proxima Nova in action on mi.com

Under the hood

.header-1 { font-family: ProximaNova, Arial, sans-serif; font-size: 36px; font-style: normal; font-weight: 300; letter-spacing: normal; line-height: 50px; text-transform: none; color: #4ACBAE; }
.content-1 { font-family: ProximaNova, Arial, sans-serif; font-size: 14px; font-style: normal; font-weight: 300; letter-spacing: normal; line-height: 30px; text-transform: none; color: #999999; }