frontend: set default font-size

The last commits introduced the '62.5% Font Size Trick' which
almost worked perfectly, except for components that do not
set font-size at all and inherit from the base font-size of
the parent.

These components now render with small 10px font-size instead
of 16px.

Fixed by changing the app style (most outer parent class) to
1.6rem which equals to 16px, so all components that do not
define font-size inherit 16px.

Author: thisconnect

frontends/web/src/style/base.css

@@ -2,6 +2,10 @@ html {
     font-size: 62.5%; /* 1rem = 10px */
 }
 
+body {
+    font-size: 1.6rem; /* 16px base for body, this will be overwritten on Android  */
+}
+
 html,
 body {
     background-color: var(--background);