Change header sizes

+ Remove header size adjustment on mobile
+ Header sizes follow the traditional typographic scale, making larger heading sizes easier to differentiate visually.

src/_Typography.sass

@@ -21,29 +21,23 @@ h6
 	margin-top: 0
 
 h1
-	font-size: 4.0rem
 	line-height: 1.2
 
 h2
-	font-size: 3.6rem
 	line-height: 1.25
 
 h3
-	font-size: 3.0rem
 	line-height: 1.3
 
 h4
-	font-size: 2.4rem
 	letter-spacing: -.08rem
 	line-height: 1.35
 
 h5
-	font-size: 1.8rem
 	letter-spacing: -.05rem
 	line-height: 1.5
 
 h6
-	font-size: 1.6rem
 	letter-spacing: 0
 	line-height: 1.4
 
@@ -51,19 +45,19 @@ h6
 @media (min-width: 40.0rem) // Safari desktop has a bug using `rem`, but Safari mobile works
 
 	h1
-		font-size: 5.0rem
+		font-size: 4.8rem
 
 	h2
-		font-size: 4.2rem
-
-	h3
 		font-size: 3.6rem
 
-	h4
-		font-size: 3.0rem
-
-	h5
+	h3
 		font-size: 2.4rem
 
+	h4
+		font-size: 2.1rem
+
+	h5
+		font-size: 1.8rem
+
 	h6
-		font-size: 1.5rem
+		font-size: 1.4rem