Add Parameterized SCSS Mixins as a css til

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 For a steady stream of TILs from a variety of rocketeers, checkout
 [til.hashrocket.com](https://til.hashrocket.com/).
 
-_585 TILs and counting..._
+_586 TILs and counting..._
 
 ---
 
@@ -83,6 +83,7 @@ _585 TILs and counting..._
 - [Dry Up SCSS With Mixins](css/dry-up-scss-with-mixins.md)
 - [Lighten And Darken With CSS Brightness Filter](css/lighten-and-darken-with-css-brightness-filter.md)
 - [Lighten And Darken With SCSS](css/lighten-and-darken-with-scss.md)
+- [Parameterized SCSS Mixins](css/parameterized-scss-mixins.md)
 
 ### Devops
 

css/parameterized-scss-mixins.md

@@ -0,0 +1,36 @@
+# Parameterized SCSS Mixins
+
+A mixin can be made to be much more versatile by parameterizing it. If you
+need variations of a block of CSS, then move the parts that vary out into
+parameters to the mixin.
+
+```css
+@mixin navigation($background-color, $color, $link-color) {
+  nav {
+    display: flex;
+    justify-content: space-around;
+    background-color: $background-color;
+    color: $color;
+
+    ul {
+      list-style: none;
+
+      li a {
+        text-decoration: none;
+        color: $link-color;
+      }
+    }
+  }
+}
+
+div.base-nav {
+  @include navgation(#fff, #444, #222);
+}
+
+div.admin-nav {
+  @include navgation(#000, #fff, #ddd);
+}
+```
+
+The mixin can now easily be used to customize different segments of your
+app's styling.