Issue with font size not working in the custom section

Hello,

I imported the newsroom theme and installed a child theme.

I'm trying to change the general font size for my website but when I change it in the theme custom section and go to base font, it doesn't work.
If I inspect, it shows me 1rem size, and apparently this comes from reboot.css
When I look at this reboot.scss through browser inspect, it says

body {
margin: 0; // 1
font-family: $font-family-base;
@include font-size($font-size-base);
font-weight: $font-weight-base;
line-height: $line-height-base;
color: $body-color;
text-align: left; // 3
background-color: $body-bg; // 2
}

Shouldn't these variables be replaced with the values from the custom section when I inspect it?
How can I set my overall body font size to 1.2rem ?