diff --git a/codemirror/addon/selection/active-line.js b/codemirror/addon/selection/active-line.js
new file mode 100644
index 00000000..22da2e0a
--- /dev/null
+++ b/codemirror/addon/selection/active-line.js
@@ -0,0 +1,71 @@
+// CodeMirror, copyright (c) by Marijn Haverbeke and others
+// Distributed under an MIT license: http://codemirror.net/LICENSE
+
+// Because sometimes you need to style the cursor's line.
+//
+// Adds an option 'styleActiveLine' which, when enabled, gives the
+// active line's wrapping <div> the CSS class "CodeMirror-activeline",
+// and gives its background <div> the class "CodeMirror-activeline-background".
+
+(function(mod) {
+  if (typeof exports == "object" && typeof module == "object") // CommonJS
+    mod(require("../../lib/codemirror"));
+  else if (typeof define == "function" && define.amd) // AMD
+    define(["../../lib/codemirror"], mod);
+  else // Plain browser env
+    mod(CodeMirror);
+})(function(CodeMirror) {
+  "use strict";
+  var WRAP_CLASS = "CodeMirror-activeline";
+  var BACK_CLASS = "CodeMirror-activeline-background";
+
+  CodeMirror.defineOption("styleActiveLine", false, function(cm, val, old) {
+    var prev = old && old != CodeMirror.Init;
+    if (val && !prev) {
+      cm.state.activeLines = [];
+      updateActiveLines(cm, cm.listSelections());
+      cm.on("beforeSelectionChange", selectionChange);
+    } else if (!val && prev) {
+      cm.off("beforeSelectionChange", selectionChange);
+      clearActiveLines(cm);
+      delete cm.state.activeLines;
+    }
+  });
+
+  function clearActiveLines(cm) {
+    for (var i = 0; i < cm.state.activeLines.length; i++) {
+      cm.removeLineClass(cm.state.activeLines[i], "wrap", WRAP_CLASS);
+      cm.removeLineClass(cm.state.activeLines[i], "background", BACK_CLASS);
+    }
+  }
+
+  function sameArray(a, b) {
+    if (a.length != b.length) return false;
+    for (var i = 0; i < a.length; i++)
+      if (a[i] != b[i]) return false;
+    return true;
+  }
+
+  function updateActiveLines(cm, ranges) {
+    var active = [];
+    for (var i = 0; i < ranges.length; i++) {
+      var range = ranges[i];
+      if (!range.empty()) continue;
+      var line = cm.getLineHandleVisualStart(range.head.line);
+      if (active[active.length - 1] != line) active.push(line);
+    }
+    if (sameArray(cm.state.activeLines, active)) return;
+    cm.operation(function() {
+      clearActiveLines(cm);
+      for (var i = 0; i < active.length; i++) {
+        cm.addLineClass(active[i], "wrap", WRAP_CLASS);
+        cm.addLineClass(active[i], "background", BACK_CLASS);
+      }
+      cm.state.activeLines = active;
+    });
+  }
+
+  function selectionChange(cm, sel) {
+    updateActiveLines(cm, sel.ranges);
+  }
+});
diff --git a/edit.html b/edit.html
index 3e976788..1d690eb0 100644
--- a/edit.html
+++ b/edit.html
@@ -11,6 +11,7 @@
 		<script src="codemirror/addon/dialog/dialog.js"></script>
 		<script src="codemirror/addon/search/searchcursor.js"></script>
 		<script src="codemirror/addon/search/search.js"></script>
+		<script src="codemirror/addon/selection/active-line.js"></script>
 
 		<link rel="stylesheet" href="codemirror/addon/fold/foldgutter.css" />
 		<script src="codemirror/addon/fold/foldcode.js"></script>
diff --git a/edit.js b/edit.js
index 69a9f62c..b5d093be 100644
--- a/edit.js
+++ b/edit.js
@@ -136,6 +136,7 @@ function initCodeMirror() {
 		gutters: ["CodeMirror-linenumbers", "CodeMirror-foldgutter", "CodeMirror-lint-markers"],
 		matchBrackets: true,
 		lint: CodeMirror.lint.css,
+		styleActiveLine: true,
 		theme: "default",
 		keyMap: isWindowsOS ? "sublime" : "default",
 		extraKeys: { // independent of current keyMap