move font-size to body

lms/static/sass/base/_base.scss

@@ -7,7 +7,6 @@
 
 html {
   font-family: $font-family-sans-serif;
-  font-size: $font-size-base;
   font-style: normal;
   line-height: 1em;
   background: theme-color("inverse");
@@ -17,6 +16,7 @@ html {
 body {
   font-family: $font-family-sans-serif;
   font-style: normal;
+  font-size: $font-size-base;
   line-height: 1em;
   background: $body-bg;