fix(static/css/poole): Contrast issues

Ensures that the contrast ratio is at least 4.5:1 (so that is complies with WCAG 2.0: https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-contrast.html).

static/css/poole.css

 
 /* No `:visited` state is required by default (browsers will use `a`) */
 a {
-  color: #268bd2;
+  color: #227bb9;
   text-decoration: none;
 }
 /* `:focus` is linked to `:hover` for basic accessibility */
 code {
   padding: .25em .5em;
   font-size: 85%;
-  color: #bf616a;
+  color: #b3555e;
   background-color: #f9f9f9;
   border-radius: 3px;
 }
   display: block;
   margin-top: -.5rem;
   margin-bottom: 1rem;
-  color: #9a9a9a;
+  color: #757575;
 }
 
 /* Related posts */
   color: #999;
 }
 .related-posts li a:hover {
-  color: #268bd2;
+  color: #227bb9;
   text-decoration: none;
 }
 .related-posts li a:hover small {