Hello,
1) Check the Infinite Scroll now. I have edited scroll settings http://prntscr.com/s38hv5
2) You call only the regular weight (400) of the Josefin Sans font http://prntscr.com/s38gix
That’s why 300 does not work for you.
So, if you want to use 300 weight for some elements only then use font-face or import https://css-tricks.com/snippets/css/using-font-face/ to call it and only after that apply CSS styles for the elements.
Regards