Only assign typey variables if not already assigned

fork-versions/default/_variables.scss

@@ -8,35 +8,35 @@
 $support-for: (
   ie:      9,
   '*':     -4,
-);
+) !default;
 
 // The font size set on the root html element.
-$base-font-size: 16px;
+$base-font-size: 16px !default;
 
 // The base line height determines the basic unit of vertical rhythm.
-$base-line-height: 24px;
+$base-line-height: 24px !default;
 
 // The length unit in which to output vertical rhythm values.
 // Supported values: px, em, rem.
-$base-unit: 'em';
+$base-unit: 'em' !default;
 
 // The default font family.
-$base-font-family: sans-serif;
+$base-font-family: sans-serif !default;
 
 // The font sizes for h1-h6.
-$h1-font-size: 2    * $base-font-size;
-$h2-font-size: 1.5  * $base-font-size;
-$h3-font-size: 1.17 * $base-font-size;
-$h4-font-size: 1    * $base-font-size;
-$h5-font-size: 0.83 * $base-font-size;
-$h6-font-size: 0.67 * $base-font-size;
+$h1-font-size: 2    * $base-font-size !default;
+$h2-font-size: 1.5  * $base-font-size !default;
+$h3-font-size: 1.17 * $base-font-size !default;
+$h4-font-size: 1    * $base-font-size !default;
+$h5-font-size: 0.83 * $base-font-size !default;
+$h6-font-size: 0.67 * $base-font-size !default;
 
 // The amount lists and blockquotes are indented.
-$indent-amount: 40px;
+$indent-amount: 40px !default;
 
 // The following variable controls whether normalize-scss will output
 // font-sizes, line-heights and block-level top/bottom margins that form a basic
 // vertical rhythm on the page, which differs from the original Normalize.css.
 // However, changing any of the variables above will cause
 // $normalize-vertical-rhythm to be automatically set to true.
-$normalize-vertical-rhythm: false;
+$normalize-vertical-rhythm: false !default;

fork-versions/typey/_variables.scss

@@ -8,23 +8,23 @@
 $support-for: (
   ie:  9,  // IE 9-11
   '*': -4, // The last 4 versions of all other browsers.
-);
+) !default;
 
 // The font size set on the root html element.
-$base-font-size: 16px;
+$base-font-size: 16px !default;
 
 // The base line height determines the basic unit of vertical rhythm.
-$base-line-height: 24px;
+$base-line-height: 24px !default;
 
 // The length unit in which to output font size and margin values.
 // Supported values: px, em, rem.
-$base-unit: 'rem';
+$base-unit: 'rem' !default;
 
 // px fallbacks for rem units are needed for IE 8 and earlier.
-$rem-fallback: false;
+$rem-fallback: false !default;
 
 // The default font family.
-$base-font-family: sans-serif;
+$base-font-family: sans-serif !default;
 
 // The font sizes for h1-h6 expressed as tee shirt sizes.
 $font-size: (
@@ -34,10 +34,10 @@ $font-size: (
   m:   $base-font-size,
   s:   14px,
   xs:  10px,
-);
+) !default;
 
 // The amount lists and blockquotes are indented.
-$indent-amount: 40px;
+$indent-amount: 40px !default;
 
 // The following variable controls whether normalize-scss will output
 // font-sizes, line-heights and block-level top/bottom margins that form a basic