Add centralised theme

Fix #110

editions/tw5.com/tiddlywiki.info

@@ -6,6 +6,7 @@
 		"tiddlywiki/snowwhite",
 		"tiddlywiki/starlight",
 		"tiddlywiki/stickytitles",
+		"tiddlywiki/centralised",
 		"giffmex/rocker",
 		"giffmex/blue",
 		"giffmex/blanca"

themes/tiddlywiki/centralised/plugin.info

@@ -0,0 +1,10 @@
+{
+	"title": "$:/themes/tiddlywiki/centralised",
+	"name": "Centralised",
+	"author": "JeremyRuston",
+	"version": "0.0.0",
+	"core-version": ">=5.0.0",
+	"plugin-type": "theme",
+	"description": "Experimental theme with a centred text column",
+	"dependents": ["$:/themes/tiddlywiki/snowwhite"]
+}

themes/tiddlywiki/centralised/styles.tid

@@ -0,0 +1,25 @@
+title: $:/themes/tiddlywiki/centralised/styles.tid
+tags: [[$:/tags/stylesheet]]
+
+\rules only filteredtranscludeinline transcludeinline macrodef macrocallinline
+
+@media (min-width: 55em) {
+
+	.tw-page-container {
+		text-align: center;
+	}
+
+	.story-river {
+		width: 55em;
+		padding: 3em;
+		margin: 0 auto;
+		text-align: left;
+	}
+
+	.sidebar-header {
+		text-align: left;
+		left: 50%;
+		right: 0;
+		padding-left: 29.5em;
+	}
+}