Lato in action on slack.com

Under the hood

.header-1 { font-family: Lato, sans-serif; font-size: 48px; font-style: normal; font-weight: 900; letter-spacing: -1px; line-height: 60px; text-transform: none; color: #4D394B; }
.content-1 { font-family: Lato, sans-serif; font-size: 24px; font-style: normal; font-weight: normal; letter-spacing: normal; line-height: 20px; text-transform: none; color: #555459; }
.content-2 { font-family: Lato, sans-serif; font-size: 20px; font-style: normal; font-weight: normal; letter-spacing: normal; line-height: 24px; text-transform: none; color: #9E9EA6; }
.content-3 { font-family: Lato, sans-serif; font-size: 24px; font-style: normal; font-weight: bold; letter-spacing: normal; line-height: 32px; text-transform: none; color: #555459; }
.content-4 { font-family: Lato, sans-serif; font-size: 20px; font-style: normal; font-weight: normal; letter-spacing: normal; line-height: 24px; text-transform: none; color: #9E9EA6; }