It's -> its when appropriate

docs/blankslate.md

@@ -37,7 +37,7 @@ When it helps the message, include `.mega-octicon`s as the first elements in the
 
 ## Variations
 
-Add an additional optional class to the `.blankslate` to change it's appearance.
+Add an additional optional class to the `.blankslate` to change its appearance.
 
 ### Fixed width
 

docs/guidelines.md

@@ -191,7 +191,7 @@ Here, we have two desktop bundles to support IE9's maximum selector limit per CS
 
 ### Including (S)CSS files
 
-Use [Sprockets](https://github.com/sstephenson/sprockets) to **require** files. However, you should explicitly **import** any scss that does not generate styles (`globals/`) in the particular SCSS file you'll be needing it's helpers in.  Here's a good example:
+Use [Sprockets](https://github.com/sstephenson/sprockets) to **require** files. However, you should explicitly **import** any scss that does not generate styles (`globals/`) in the particular SCSS file you'll be needing its helpers in.  Here's a good example:
 
 {% highlight scss %}
 //= require_tree ./plugins

docs/nav.md

@@ -118,7 +118,7 @@ Additional bits of text and links can be styled for optimal placement with `.tab
 
 ## Filter list
 
-A vertical list of filters. Grey text on white background. Selecting a filter from the list will fill it's background with blue and make the text white.
+A vertical list of filters. Grey text on white background. Selecting a filter from the list will fill its background with blue and make the text white.
 
 {% example html %}
 <ul class="filter-list">