[landing] Fix "fluid" font-size/padding-bottom for info-block:title

Summary: Interpolate over values from width of 320px to 1850px

Test Plan:
Continues to look as expected:

Reviewers: benschac, palys-swm, ashoat

Reviewed By: ashoat

Subscribers: Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3437