style(guide-list): remove margin on small screens (#311)

- This allows the nav-list to reach full width of container
- This increases the wide-screen margin to better match other constants in the app

Author: willshowell

src/app/pages/guide-list/guide-list.scss

@@ -1,12 +1,18 @@
+@import '../../../styles/constants';
+
 :host {
   display: flex;
   flex-direction: column;
   flex-grow: 1;
 }
 
 .docs-guide-list {
-  margin: 50px;
   flex-grow: 1;
+  margin: $content-padding-side;
+
+  @media (max-width: $small-breakpoint-width) {
+    margin: 0;
+  }
 }
 
 .docs-guide-item, .docs-guide-item:hover {