Add new style for tabular numerals and update some styles for the main app content

Author: lulunac27a

src/App.scss

@@ -1,8 +1,9 @@
 #app {
-  font-family: Avenir, Helvetica, Arial, sans-serif;
-  -webkit-font-smoothing: antialiased;
-  -moz-osx-font-smoothing: grayscale;
-  text-align: center;
-  color: #2c3e50;
-  margin-top: 60px;
+  font-family: Avenir, Helvetica, Arial, system-ui, sans-serif; //set default font family to Avenir or system-ui or sans-serif font
+  font-variant-numeric: tabular-nums; //set numeric values to tabular numerals
+  -webkit-font-smoothing: antialiased; //set font smoothing to antialiased text in WebKit browsers
+  -moz-osx-font-smoothing: grayscale; //set font smoothing to grayscale in Firefox browsers
+  text-align: center; //center the text display content
+  color: #204060; //set text color to dark blue
+  margin-top: 50px; //set top margin to 50 pixels
 }