Override gray colours

Override the default Tailwind `gray` colours, and update anywhere that
the originals were used.

References #27

web/themes/custom/opdavies/assets/css/components/table.pcss

@@ -7,7 +7,7 @@
 
   th,
   td {
-    @apply px-4 py-2 border border-solid border-gray-300
+    @apply px-4 py-2 border border-solid border-gray-200
   }
 }
 

web/themes/custom/opdavies/assets/css/custom-base.pcss

@@ -19,7 +19,7 @@ a {
 }
 
 blockquote {
-  @apply pl-5 border-l-4 border-gray-300 italic
+  @apply pl-5 border-l-4 border-gray-200 italic
 }
 
 iframe {

web/themes/custom/opdavies/tailwind.config.js

@@ -59,7 +59,17 @@ module.exports = {
     }),
     extend: {
       colors: {
-        inherit: 'inherit'
+        inherit: 'inherit',
+
+        gray: {
+          50: "#f9f9f9",
+          100: "#f5f5f5",
+          200: "#aaa",
+          700: "#36393e",
+          750: "#2e3136",
+          800: "#1e2125",
+          900: "#18171b",
+        }
       },
       fontFamily: {
         mono: [