diff --git a/examples/themes.html b/examples/themes.html
index 171d3ae..4286d2c 100644
--- a/examples/themes.html
+++ b/examples/themes.html
@@ -89,18 +89,26 @@
     rendition.on("locationChanged", function(location){
       console.log(location);
     });
+
     /*
-    rendition.themes.register({
-      "dark" : "themes.css",
-      "light" : "themes.css",
-      "tan" : "themes.css"
-    });
+    rendition.themes.register("dark", "theme.css");
+    rendition.themes.register("light", "theme.css");
+    rendition.themes.register("tan", "theme.css");
     */
-    rendition.themes.register("themes.css");
 
-    rendition.themes.apply("tan");
-    rendition.themes.fontSize("140%");
 
+    rendition.themes.default({
+      h2: {
+        'font-size': '32px',
+        color: 'purple'
+      },
+      p: {
+        "margin": '10px'
+      }
+    });
+
+    // rendition.themes.apply("tan");
+    // rendition.themes.fontSize("140%");
 
   </script>
 
diff --git a/package.json b/package.json
index ea8c295..3f1acec 100644
--- a/package.json
+++ b/package.json
@@ -18,6 +18,7 @@
     "minify": "NODE_ENV=production npm run build",
     "legacy": "NODE_ENV=production LEGACY=true npm run build",
     "compile": "./node_modules/.bin/babel --optional runtime -d lib/ src/",
+    "watch": "./node_modules/.bin/babel --watch --optional runtime -d lib/ src/",
     "prepublish": "npm run compile && npm run build && npm run minify && npm run legacy"
   },
   "author": "fchasen@gmail.com",
diff --git a/src/contents.js b/src/contents.js
index 6eba0b0..a082cce 100644
--- a/src/contents.js
+++ b/src/contents.js
@@ -461,13 +461,14 @@ class Contents {
 		}.bind(this));
 	}
 
-	// https://developer.mozilla.org/en-US/docs/Web/API/CSSStyleSheet/insertRule
+	// Array: https://developer.mozilla.org/en-US/docs/Web/API/CSSStyleSheet/insertRule
+	// Object: https://github.com/desirable-objects/json-to-css
 	addStylesheetRules(rules) {
 		var styleEl;
 		var styleSheet;
 		var key = "epubjs-inserted-css";
 
-		if(!this.document) return;
+		if(!this.document || !rules || rules.length === 0) return;
 
 		// Check if link already exists
 		styleEl = this.document.getElementById("#"+key);
@@ -482,21 +483,33 @@ class Contents {
 		// Grab style sheet
 		styleSheet = styleEl.sheet;
 
-		for (var i = 0, rl = rules.length; i < rl; i++) {
-			var j = 1, rule = rules[i], selector = rules[i][0], propStr = "";
-			// If the second argument of a rule is an array of arrays, correct our variables.
-			if (Object.prototype.toString.call(rule[1][0]) === "[object Array]") {
-				rule = rule[1];
-				j = 0;
-			}
+		if (Object.prototype.toString.call(rules) === "[object Array]") {
+			for (var i = 0, rl = rules.length; i < rl; i++) {
+				var j = 1, rule = rules[i], selector = rules[i][0], propStr = "";
+				// If the second argument of a rule is an array of arrays, correct our variables.
+				if (Object.prototype.toString.call(rule[1][0]) === "[object Array]") {
+					rule = rule[1];
+					j = 0;
+				}
 
-			for (var pl = rule.length; j < pl; j++) {
-				var prop = rule[j];
-				propStr += prop[0] + ":" + prop[1] + (prop[2] ? " !important" : "") + ";\n";
-			}
+				for (var pl = rule.length; j < pl; j++) {
+					var prop = rule[j];
+					propStr += prop[0] + ":" + prop[1] + (prop[2] ? " !important" : "") + ";\n";
+				}
 
-			// Insert CSS Rule
-			styleSheet.insertRule(selector + "{" + propStr + "}", styleSheet.cssRules.length);
+				// Insert CSS Rule
+				styleSheet.insertRule(selector + "{" + propStr + "}", styleSheet.cssRules.length);
+			}
+		} else {
+			const selectors = Object.keys(rules);
+			selectors.forEach((selector) => {
+				const definition = rules[selector];
+				const _rules = Object.keys(definition);
+				const result = _rules.map((rule) => {
+					return `${rule}:${definition[rule]}`;
+				}).join(';');
+				styleSheet.insertRule(`${selector}{${result}}`, styleSheet.cssRules.length);
+			});
 		}
 	}
 
diff --git a/src/rendition.js b/src/rendition.js
index 02c1348..15ef04e 100644
--- a/src/rendition.js
+++ b/src/rendition.js
@@ -21,6 +21,7 @@ import Contents from "./contents";
  * @param {string} options.layout
  * @param {string} options.spread
  * @param {int} options.minSpreadWidth overridden by spread: none (never) / both (always)
+ * @param {string} options.stylesheet url of stylesheet to be injected
  */
 class Rendition {
 	constructor(book, options) {
@@ -34,7 +35,8 @@ class Rendition {
 			flow: null,
 			layout: null,
 			spread: null,
-			minSpreadWidth: 800
+			minSpreadWidth: 800,
+			stylesheet: null
 		});
 
 		extend(this.settings, options);
@@ -71,6 +73,10 @@ class Rendition {
 		this.hooks.content.register(this.passEvents.bind(this));
 		this.hooks.content.register(this.adjustImages.bind(this));
 
+		if (this.settings.stylesheet) {
+			this.book.spine.hooks.content.register(this.injectStylesheet.bind(this));
+		}
+
 		// this.hooks.display.register(this.afterDisplay.bind(this));
 		this.themes = new Themes(this);
 
@@ -596,14 +602,14 @@ class Rendition {
 			});
 		}
 
-		contents.addStylesheetRules([
-			["img",
-				["max-width", (this._layout.columnWidth) + "px !important"],
-				["max-height", (this._layout.height) + "px !important"],
-				["object-fit", "contain"],
-				["page-break-inside", "avoid"]
-			]
-		]);
+		contents.addStylesheetRules({
+			"img" : {
+				"max-width": (this._layout.columnWidth) + "px !important",
+				"max-width": (this._layout.columnWidth) + "px !important",
+				"object-fit": "contain",
+				"page-break-inside": "avoid"
+			}
+		});
 		return new Promise(function(resolve, reject){
 			// Wait to apply
 			setTimeout(function() {
@@ -622,6 +628,14 @@ class Rendition {
 			this.display(relative);
 		});
 	}
+
+	injectStylesheet(doc, section) {
+		let style = doc.createElement("link");
+		style.setAttribute("type", "text/css");
+		style.setAttribute("rel", "stylesheet");
+		style.setAttribute("href", this.settings.stylesheet);
+		doc.getElementsByTagName("head")[0].appendChild(style);
+	}
 }
 
 //-- Enable binding events to Renderer
diff --git a/src/themes.js b/src/themes.js
index d4db495..3a2f7ae 100644
--- a/src/themes.js
+++ b/src/themes.js
@@ -5,7 +5,7 @@ class Themes {
 		this.rendition = rendition;
 		this._themes = {
 			"default" : {
-				"rules" : [],
+				"rules" : {},
 				"url" : "",
 				"serialized" : ""
 			}
@@ -97,7 +97,7 @@ class Themes {
 		var theme;
 
 		for (var name in themes) {
-			if (themes.hasOwnProperty(name)) {
+			if (themes.hasOwnProperty(name) && name === this._current) {
 				theme = themes[name];
 				if(theme.rules || (theme.url && links.indexOf(theme.url) === -1)) {
 					this.add(name, contents);
@@ -105,7 +105,7 @@ class Themes {
 			}
 		}
 
-		if(this._current) {
+		if(this._current != "default") {
 			contents.addClass(this._current);
 		}
 	}
@@ -121,7 +121,7 @@ class Themes {
 			contents.addStylesheet(theme.url);
 		} else if (theme.serialized) {
 			// TODO: handle serialized
-		} else if (theme.rules && theme.rules.length) {
+		} else if (theme.rules) {
 			contents.addStylesheetRules(theme.rules);
 			theme.injected = true;
 		}