diff --git a/src/components/App.vue b/src/components/App.vue
index b243f648..46766757 100644
--- a/src/components/App.vue
+++ b/src/components/App.vue
@@ -34,10 +34,10 @@ export default {
 @import 'common/app';
 
 .app__spash-screen {
-  position: absolute;
-  width: 100%;
+  margin: 0 auto;
+  max-width: 600px;
   height: 100%;
   background: no-repeat center url('../assets/logo.svg');
-  background-color: #fff;
+  background-size: contain;
 }
 </style>
diff --git a/src/components/Layout.vue b/src/components/Layout.vue
index 1f8bce75..ccf1d75f 100644
--- a/src/components/Layout.vue
+++ b/src/components/Layout.vue
@@ -1,6 +1,6 @@
 <template>
   <div class="layout">
-    <div class="layout__panel flex flex--row">
+    <div class="layout__panel flex flex--row" :class="{'flex--end': styles.showSideBar && !styles.showExplorer}">
       <div class="layout__panel layout__panel--explorer" v-show="styles.showExplorer" :style="{ width: constants.explorerWidth + 'px' }">
         <explorer></explorer>
       </div>
@@ -31,7 +31,7 @@
 </template>
 
 <script>
-import { mapState, mapGetters, mapMutations } from 'vuex';
+import { mapGetters, mapMutations } from 'vuex';
 import NavigationBar from './NavigationBar';
 import ButtonBar from './ButtonBar';
 import StatusBar from './StatusBar';
@@ -52,10 +52,8 @@ export default {
     Preview,
   },
   computed: {
-    ...mapState('layout', [
-      'constants',
-    ]),
     ...mapGetters('layout', [
+      'constants',
       'styles',
     ]),
   },
@@ -77,48 +75,12 @@ export default {
     const previewElt = this.$el.querySelector('.preview__inner-2');
     const tocElt = this.$el.querySelector('.toc__inner');
     editorSvc.init(editorElt, previewElt, tocElt);
-
-    // TOC click behaviour
-    let isMousedown;
-    function onClick(e) {
-      if (!isMousedown) {
-        return;
-      }
-      e.preventDefault();
-      const y = e.clientY - tocElt.getBoundingClientRect().top;
-
-      editorSvc.sectionDescList.some((sectionDesc) => {
-        if (y >= sectionDesc.tocDimension.endOffset) {
-          return false;
-        }
-        const posInSection = (y - sectionDesc.tocDimension.startOffset)
-          / (sectionDesc.tocDimension.height || 1);
-        const editorScrollTop = sectionDesc.editorDimension.startOffset
-          + (sectionDesc.editorDimension.height * posInSection);
-        editorElt.parentNode.scrollTop = editorScrollTop;
-        const previewScrollTop = sectionDesc.previewDimension.startOffset
-          + (sectionDesc.previewDimension.height * posInSection);
-        previewElt.parentNode.scrollTop = previewScrollTop;
-        return true;
-      });
-    }
-
-    tocElt.addEventListener('mouseup', () => {
-      isMousedown = false;
-    });
-    tocElt.addEventListener('mouseleave', () => {
-      isMousedown = false;
-    });
-    tocElt.addEventListener('mousedown', (e) => {
-      isMousedown = e.which === 1;
-      onClick(e);
-    });
-    tocElt.addEventListener('mousemove', (e) => {
-      onClick(e);
-    });
   },
   destroyed() {
     window.removeEventListener('resize', this.updateStyle);
+    window.removeEventListener('keyup', this.saveSelection);
+    window.removeEventListener('mouseup', this.saveSelection);
+    window.removeEventListener('contextmenu', this.saveSelection);
   },
 };
 </script>
@@ -152,6 +114,11 @@ export default {
   background-color: #fff;
 }
 
+.layout__panel--button-bar,
+.layout__panel--preview {
+  background-color: #f3f3f3;
+}
+
 .layout__panel--explorer,
 .layout__panel--side-bar {
   background-color: #dadada;
diff --git a/src/components/SideBar.vue b/src/components/SideBar.vue
index 8d257ce9..04cc9ba2 100644
--- a/src/components/SideBar.vue
+++ b/src/components/SideBar.vue
@@ -1,13 +1,11 @@
 <template>
   <div class="side-bar flex flex--column">
-    <div class="side-title flex flex--row flex--space-between">
-      <div class="flex flex--row">
-        <button v-if="panel !== 'menu'" class="side-title__button button" @click="panel = 'menu'">
-          <icon-arrow-left></icon-arrow-left>
-        </button>
-        <div class="side-title__title">
-          {{panelName}}
-        </div>
+    <div class="side-title flex flex--row">
+      <button v-if="panel !== 'menu'" class="side-title__button button" @click="panel = 'menu'">
+        <icon-arrow-left></icon-arrow-left>
+      </button>
+      <div class="side-title__title">
+        {{panelName}}
       </div>
       <button class="side-title__button button" @click="toggleSideBar(false)">
         <icon-close></icon-close>
@@ -15,19 +13,22 @@
     </div>
     <div class="side-bar__inner">
       <div v-if="panel === 'menu'" class="side-bar__panel side-bar__panel--menu">
-        <menu-item>
+        <side-bar-item @click.native="signin">
           <icon-login slot="icon"></icon-login>
           <div>Sign in with Google</div>
           <span>Have all your files and settings backed up and synced.</span>
-        </menu-item>
-        <menu-item @click.native="panel = 'toc'">
+        </side-bar-item>
+        <side-bar-item @click.native="panel = 'toc'">
           <icon-toc slot="icon"></icon-toc>
-          Table of Contents
-        </menu-item>
-        <menu-item @click.native="panel = 'help'">
+          Table of contents
+        </side-bar-item>
+        <side-bar-item @click.native="panel = 'help'">
           <icon-help-circle slot="icon"></icon-help-circle>
-          Markdown help
-        </menu-item>
+          Markdown cheat sheet
+        </side-bar-item>
+      </div>
+      <div v-else-if="panel === 'help'" class="side-bar__panel side-bar__panel--help">
+        <pre class="markdown-highlighting" v-html="markdownSample"></pre>
       </div>
       <div class="side-bar__panel side-bar__panel--toc" :class="{'side-bar__panel--hidden': panel !== 'toc'}">
         <toc>
@@ -40,25 +41,30 @@
 <script>
 import { mapActions } from 'vuex';
 import Toc from './Toc';
-import MenuItem from './MenuItem';
+import SideBarItem from './SideBarItem';
+import markdownSample from '../data/markdownSample.md';
+import markdownConversionSvc from '../services/markdownConversionSvc';
+import userSvc from '../services/userSvc';
 
 const panelNames = {
   menu: 'Menu',
-  help: 'Markdown help',
-  toc: 'Table of Contents',
+  help: 'Markdown cheat sheet',
+  toc: 'Table of contents',
 };
 
 export default {
   components: {
     Toc,
-    MenuItem,
+    SideBarItem,
   },
   data: () => ({
     panel: 'menu',
     panelNames: {
       menu: 'Menu',
       toc: 'Table of Contents',
+      help: 'Markdown cheat sheet',
     },
+    markdownSample: markdownConversionSvc.highlight(markdownSample),
   }),
   computed: {
     panelName() {
@@ -69,6 +75,9 @@ export default {
     ...mapActions('data', [
       'toggleSideBar',
     ]),
+    signin() {
+      userSvc.signinWithGoogle();
+    },
   },
 };
 </script>
@@ -82,18 +91,38 @@ export default {
 }
 
 .side-bar__inner {
-  overflow: auto;
+  position: relative;
   height: 100%;
-  padding: 10px 0;
 }
 
 .side-bar__panel {
   position: absolute;
   width: 100%;
   height: 100%;
+  overflow: auto;
 }
 
 .side-bar__panel--hidden {
   left: 1000px;
 }
+
+.side-bar__panel--help {
+  padding: 0 10px 40px 20px;
+
+  pre {
+    font-size: 0.9em;
+    font-variant-ligatures: no-common-ligatures;
+    line-height: 1.25;
+    white-space: pre-wrap;
+    word-break: break-word;
+    word-wrap: break-word;
+  }
+
+  .code,
+  .img,
+  .imgref,
+  .cl-toc {
+    background-color: rgba(0, 0, 0, 0.05);
+  }
+}
 </style>
diff --git a/src/components/MenuItem.vue b/src/components/SideBarItem.vue
similarity index 72%
rename from src/components/MenuItem.vue
rename to src/components/SideBarItem.vue
index c08dfcc0..5f991512 100644
--- a/src/components/MenuItem.vue
+++ b/src/components/SideBarItem.vue
@@ -1,6 +1,6 @@
 <template>
-  <div class="menu-item button flex flex--row flex--align-center">
-    <div class="menu-item__icon flex flex--column flex--center">
+  <div class="side-bar-item button flex flex--row flex--align-center">
+    <div class="side-bar-item__icon flex flex--column flex--center">
       <slot name="icon"></slot>
     </div>
     <div class="flex flex--column">
@@ -10,7 +10,7 @@
 </template>
 
 <style lang="scss">
-.menu-item {
+.side-bar-item {
   text-align: left;
   padding: 10px 12px;
   height: auto;
@@ -25,7 +25,7 @@
   }
 }
 
-.menu-item__icon {
+.side-bar-item__icon {
   height: 20px;
   width: 20px;
   margin-right: 12px;
diff --git a/src/components/Toc.vue b/src/components/Toc.vue
index 254d5b76..e695d9bd 100644
--- a/src/components/Toc.vue
+++ b/src/components/Toc.vue
@@ -4,3 +4,98 @@
     </div>
   </div>
 </template>
+
+<script>
+import editorSvc from '../services/editorSvc';
+
+export default {
+  mounted() {
+    const tocElt = this.$el.querySelector('.toc__inner');
+
+    // TOC click behaviour
+    let isMousedown;
+    function onClick(e) {
+      if (!isMousedown) {
+        return;
+      }
+      e.preventDefault();
+      const y = e.clientY - tocElt.getBoundingClientRect().top;
+
+      editorSvc.sectionDescList.some((sectionDesc) => {
+        if (y >= sectionDesc.tocDimension.endOffset) {
+          return false;
+        }
+        const posInSection = (y - sectionDesc.tocDimension.startOffset)
+          / (sectionDesc.tocDimension.height || 1);
+        const editorScrollTop = sectionDesc.editorDimension.startOffset
+          + (sectionDesc.editorDimension.height * posInSection);
+        editorSvc.editorElt.parentNode.scrollTop = editorScrollTop;
+        const previewScrollTop = sectionDesc.previewDimension.startOffset
+          + (sectionDesc.previewDimension.height * posInSection);
+        editorSvc.previewElt.parentNode.scrollTop = previewScrollTop;
+        return true;
+      });
+    }
+
+    tocElt.addEventListener('mouseup', () => {
+      isMousedown = false;
+    });
+    tocElt.addEventListener('mouseleave', () => {
+      isMousedown = false;
+    });
+    tocElt.addEventListener('mousedown', (e) => {
+      isMousedown = e.which === 1;
+      onClick(e);
+    });
+    tocElt.addEventListener('mousemove', (e) => {
+      onClick(e);
+    });
+  },
+};
+</script>
+
+<style lang="scss">
+.toc__inner {
+  color: rgba(0, 0, 0, 0.75);
+  cursor: pointer;
+  font-size: 10px;
+  padding: 10px 20px;
+  white-space: nowrap;
+  -webkit-user-select: none;
+  -moz-user-select: none;
+  -ms-user-select: none;
+  user-select: none;
+
+  * {
+    font-weight: inherit;
+    pointer-events: none;
+  }
+
+  .cl-toc-section {
+    * {
+      margin: 0.25em 0;
+      padding: 0.25em 0;
+    }
+
+    h2 {
+      margin-left: 8px;
+    }
+
+    h3 {
+      margin-left: 16px;
+    }
+
+    h4 {
+      margin-left: 24px;
+    }
+
+    h5 {
+      margin-left: 32px;
+    }
+
+    h6 {
+      margin-left: 40px;
+    }
+  }
+}
+</style>
diff --git a/src/components/common/app.scss b/src/components/common/app.scss
index 4ff2c299..3c2086de 100644
--- a/src/components/common/app.scss
+++ b/src/components/common/app.scss
@@ -3,7 +3,7 @@
 @import './markdownHighlighting';
 
 body {
-  background-color: #f3f3f3;
+  background-color: #fff;
   top: 0;
   right: 0;
   bottom: 0;
@@ -110,6 +110,11 @@ textarea {
   justify-content: center;
 }
 
+.flex--end {
+  -webkit-justify-content: flex-end;
+  justify-content: flex-end;
+}
+
 .flex--space-between {
   -webkit-justify-content: space-between;
   justify-content: space-between;
@@ -123,7 +128,7 @@ textarea {
 .side-title {
   height: 44px;
   line-height: 36px;
-  padding: 4px 6px 0;
+  padding: 4px 4px 0;
   background-color: rgba(0, 0, 0, 0.1);
   -webkit-flex: none;
   flex: none;
@@ -136,6 +141,8 @@ textarea {
   display: inline-block;
   background-color: transparent;
   opacity: 0.75;
+  -webkit-flex: none;
+  flex: none;
 
   /* prevent from seeing wrapped buttons */
   margin-bottom: 20px;
@@ -150,4 +157,8 @@ textarea {
 .side-title__title {
   text-transform: uppercase;
   padding: 0 5px;
+  overflow: hidden;
+  white-space: nowrap;
+  text-overflow: ellipsis;
+  width: 100%;
 }
diff --git a/src/data/markdownSample.md b/src/data/markdownSample.md
index 01ad688b..889779d3 100644
--- a/src/data/markdownSample.md
+++ b/src/data/markdownSample.md
@@ -1,5 +1,5 @@
 Headers
-----------------------------
+---------------------------
 
 # Header 1
 
@@ -9,7 +9,7 @@ Headers
 
 
 Styling
-----------------------------
+---------------------------
 
 *Emphasize* _emphasize_
 
@@ -25,7 +25,7 @@ H~2~O is a liquid.
 
 
 Lists
-----------------------------
+---------------------------
 
 - Item
 * Item
@@ -37,7 +37,7 @@ Lists
 
 
 Links
-----------------------------
+---------------------------
 
 A [link](http://example.com).
 
@@ -45,7 +45,7 @@ An image: ![Alt](img.jpg)
 
 
 Code
-----------------------------
+---------------------------
 
 Some `inline code`.
 
@@ -61,7 +61,7 @@ var foo = 'bar';
 
 
 Tables
-----------------------------
+---------------------------
 
 Item     | Value
 -------- | -----
@@ -76,7 +76,7 @@ Pipe     | $1
 
 
 Definition lists
-----------------------------
+---------------------------
 
 Markdown
 :  Text-to-HTML conversion tool
@@ -86,7 +86,7 @@ Classeur
 :  A Markdown editing app
 
 Footnotes
-----------------------------
+---------------------------
 
 Some text with a footnote.[^1]
 
@@ -94,7 +94,7 @@ Some text with a footnote.[^1]
 
 
 Abbreviations
-----------------------------
+---------------------------
 
 Markdown converts text to HTML.
 
@@ -102,7 +102,7 @@ Markdown converts text to HTML.
 
 
 LaTeX math
-----------------------------
+---------------------------
 
 The Gamma function satisfying $\Gamma(n) = (n-1)!\quad\forall
 n\in\mathbb N$ is via the Euler integral
diff --git a/src/index.js b/src/index.js
index 700f85f2..ad4bde94 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,10 +1,10 @@
 import Vue from 'vue';
-import App from './components/App';
-import store from './store';
-import './services/syncSvc';
 import './extensions/';
+import './services/syncSvc';
 import './services/optional';
 import './icons/';
+import App from './components/App';
+import store from './store';
 
 Vue.config.productionTip = false;
 
diff --git a/src/services/localDbSvc.js b/src/services/localDbSvc.js
index 6b96eabb..2067379b 100644
--- a/src/services/localDbSvc.js
+++ b/src/services/localDbSvc.js
@@ -93,10 +93,6 @@ class Connection {
     request.onsuccess = () => {
       tx.txCounter = request.result ? request.result.tx : 0;
       tx.txCounter += 1;
-      dbStore.put({
-        id: 'txCounter',
-        tx: tx.txCounter,
-      });
       cb(tx);
     };
   }
@@ -137,45 +133,38 @@ export default {
    * Read and apply all changes from the DB since previous transaction.
    */
   readAll(storeItemMap, tx, cb) {
-    let resetMap;
-
-    // We may have missed some delete markers
-    if (this.lastTx && tx.txCounter - this.lastTx > deleteMarkerMaxAge) {
-      // Delete all dirty store items (user was asleep anyway...)
-      resetMap = true;
-      // And retrieve everything from DB
-      this.lastTx = 0;
-    }
-
+    let lastTx = this.lastTx;
     const dbStore = tx.objectStore(dbStoreName);
     const index = dbStore.index('tx');
     const range = window.IDBKeyRange.lowerBound(this.lastTx, true);
-    const items = [];
-    const itemsToDelete = [];
+    const changes = [];
     index.openCursor(range).onsuccess = (event) => {
       const cursor = event.target.result;
       if (cursor) {
         const item = cursor.value;
-        items.push(item);
-        // Remove old delete markers
-        if (!item.updated && tx.txCounter - item.tx > deleteMarkerMaxAge) {
-          itemsToDelete.push(item);
+        if (item.tx > lastTx) {
+          lastTx = item.tx;
+          if (this.lastTx && item.tx - this.lastTx > deleteMarkerMaxAge) {
+            // We may have missed some delete markers
+            window.location.reload();
+            return;
+          }
         }
+        // Collect change
+        changes.push(item);
         cursor.continue();
       } else {
-        itemsToDelete.forEach((item) => {
-          dbStore.delete(item.id);
+        if (changes.length) {
+          dbg(`Got ${changes.length} changes`);
+        }
+        changes.forEach((item) => {
+          this.readDbItem(item, storeItemMap);
+          // If item is an old delete marker, remove it from the DB
+          if (!item.updated && lastTx - item.tx > deleteMarkerMaxAge) {
+            dbStore.delete(item.id);
+          }
         });
-        if (items.length) {
-          dbg(`Got ${items.length} items`);
-        }
-        if (resetMap) {
-          Object.keys(storeItemMap).forEach((id) => {
-            delete storeItemMap[id];
-          });
-          this.updatedMap = Object.create(null);
-        }
-        items.forEach(item => this.readDbItem(item, storeItemMap));
+        this.lastTx = lastTx;
         cb();
       }
     };
@@ -185,8 +174,8 @@ export default {
    * Write all changes from the store since previous transaction.
    */
   writeAll(storeItemMap, tx) {
-    this.lastTx = tx.txCounter;
     const dbStore = tx.objectStore(dbStoreName);
+    const incrementedTx = this.lastTx + 1;
 
     // Remove deleted store items
     Object.keys(this.updatedMap).forEach((id) => {
@@ -194,9 +183,10 @@ export default {
         // Put a delete marker to notify other tabs
         dbStore.put({
           id,
-          tx: this.lastTx,
+          tx: incrementedTx,
         });
         delete this.updatedMap[id];
+        this.lastTx = incrementedTx; // No need to read what we just wrote
       }
     });
 
@@ -207,11 +197,12 @@ export default {
       if (this.updatedMap[storeItem.id] !== storeItem.updated) {
         const item = {
           ...storeItem,
-          tx: this.lastTx,
+          tx: incrementedTx,
         };
         dbg('Putting 1 item');
         dbStore.put(item);
         this.updatedMap[item.id] = item.updated;
+        this.lastTx = incrementedTx; // No need to read what we just wrote
       }
     });
   },
@@ -220,18 +211,18 @@ export default {
    * Read and apply one DB change.
    */
   readDbItem(dbItem, storeItemMap) {
-    const existingStoreItem = storeItemMap[dbItem.id];
     if (!dbItem.updated) {
+      // DB item is a delete marker
       delete this.updatedMap[dbItem.id];
+      const existingStoreItem = storeItemMap[dbItem.id];
       if (existingStoreItem) {
+        delete storeItemMap[existingStoreItem.id];
+        // Remove object from the store
         const prefix = getStorePrefixFromType(existingStoreItem.type);
-        if (prefix) {
-          delete storeItemMap[existingStoreItem.id];
-          // Remove object from the store
-          store.commit(`${prefix}/deleteItem`, existingStoreItem.id);
-        }
+        store.commit(`${prefix}/deleteItem`, existingStoreItem.id);
       }
     } else if (this.updatedMap[dbItem.id] !== dbItem.updated) {
+      // DB item is different from the corresponding store item
       this.updatedMap[dbItem.id] = dbItem.updated;
       storeItemMap[dbItem.id] = dbItem;
       // Put object in the store
diff --git a/src/services/markdownConversionSvc.js b/src/services/markdownConversionSvc.js
index 32bad598..4b294a6e 100644
--- a/src/services/markdownConversionSvc.js
+++ b/src/services/markdownConversionSvc.js
@@ -255,6 +255,20 @@ const markdownConversionSvc = {
       htmlSectionDiff,
     };
   },
+
+  /**
+   * Helper to highlight arbitrary markdown
+   * @param {Object} markdown The markdown content to highlight.
+   * @param {Object} converter An optional converter.
+   * @param {Object} grammars Optional grammars.
+   * @returns {Object} The highlighted markdown in HTML format.
+   */
+  highlight(markdown, converter = this.defaultConverter, grammars = this.defaultPrismGrammars) {
+    const parsingCtx = this.parseSections(converter, markdown);
+    return parsingCtx.sections.map(
+      section => Prism.highlight(section.text, grammars[section.data]),
+    ).join('');
+  },
 };
 
 markdownConversionSvc.defaultConverter = markdownConversionSvc.createConverter(defaultOptions);
diff --git a/src/services/userSvc.js b/src/services/userSvc.js
new file mode 100644
index 00000000..9a9f0083
--- /dev/null
+++ b/src/services/userSvc.js
@@ -0,0 +1,63 @@
+import utils from './utils';
+
+const googleClientId = '241271498917-t4t7d07qis7oc0ahaskbif3ft6tk63cd.apps.googleusercontent.com';
+const appUri = 'http://localhost:8080/';
+const googleAppsDomain = null;
+const origin = `${location.protocol}//${location.host}`;
+
+export default {
+  oauth2Context: null,
+  signinWithGoogle() {
+    this.cleanOauth2Context();
+    const state = utils.uid();
+    let authorizeUrl = 'https://accounts.google.com/o/oauth2/v2/auth';
+    authorizeUrl = utils.addQueryParam(authorizeUrl, 'client_id', googleClientId);
+    authorizeUrl = utils.addQueryParam(authorizeUrl, 'response_type', 'code');
+    authorizeUrl = utils.addQueryParam(authorizeUrl, 'redirect_uri', `${appUri}oauth2/google/callback`);
+    authorizeUrl = utils.addQueryParam(authorizeUrl, 'state', state);
+    if (googleAppsDomain) {
+      authorizeUrl = utils.addQueryParam(authorizeUrl, 'scope', 'openid email');
+      authorizeUrl = utils.addQueryParam(authorizeUrl, 'hd', googleAppsDomain);
+    } else {
+      authorizeUrl = utils.addQueryParam(authorizeUrl, 'scope', 'profile email');
+    }
+    const wnd = window.open(authorizeUrl);
+    if (!wnd) {
+      return Promise.resolve();
+    }
+    return new Promise((resolve) => {
+      const msgHandler = (event) => {
+        if (event.source === wnd
+          && event.origin === origin
+          && event.data
+          && event.data.state === state
+        ) {
+          this.cleanOauth2Context();
+          console.log(event.data);
+          resolve();
+        }
+      };
+      window.addEventListener('message', msgHandler);
+      const checkClosedInterval = setInterval(() => {
+        if (this.oauth2Context && this.oauth2Context.wnd.closed) {
+          this.cleanOauth2Context();
+        }
+      }, 200);
+      this.oauth2Context = {
+        wnd,
+        msgHandler,
+        checkClosedInterval,
+      };
+    });
+  },
+  cleanOauth2Context() {
+    if (this.oauth2Context) {
+      clearInterval(this.oauth2Context.checkClosedInterval);
+      if (!this.oauth2Context.wnd.closed) {
+        this.oauth2Context.wnd.close();
+      }
+      window.removeEventListener('message', this.oauth2Context.msgHandler);
+      this.oauth2Context = null;
+    }
+  },
+};
diff --git a/src/services/utils.js b/src/services/utils.js
index ac09abf8..71c99d23 100644
--- a/src/services/utils.js
+++ b/src/services/utils.js
@@ -2,6 +2,7 @@ const crypto = window.crypto || window.msCrypto;
 const alphabet = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('');
 const radix = alphabet.length;
 const array = new Uint32Array(20);
+const urlParser = window.document.createElement('a');
 
 export default {
   uid() {
@@ -12,4 +13,17 @@ export default {
     const randomizedInterval = Math.floor((1 + ((Math.random() - 0.5) * 0.1)) * interval);
     setInterval(() => func(), randomizedInterval);
   },
+  addQueryParam(url, key, value) {
+    if (!url || !key || !value) {
+      return url;
+    }
+    urlParser.href = url;
+    if (urlParser.search) {
+      urlParser.search += '&';
+    } else {
+      urlParser.search = '?';
+    }
+    urlParser.search += `${encodeURIComponent(key)}=${encodeURIComponent(value)}`;
+    return urlParser.href;
+  },
 };
diff --git a/src/store/modules/layout.js b/src/store/modules/layout.js
index c788e3e6..f0970d45 100644
--- a/src/store/modules/layout.js
+++ b/src/store/modules/layout.js
@@ -7,6 +7,97 @@ const navigationBarLeftWidth = 570;
 const maxTitleMaxWidth = 800;
 const minTitleMaxWidth = 200;
 
+const constants = {
+  explorerWidth: 250,
+  sideBarWidth: 280,
+  navigationBarHeight: 44,
+  buttonBarWidth: 30,
+  statusBarHeight: 20,
+};
+
+function computeStyles(state, localSettings, styles = {
+  showNavigationBar: !localSettings.showEditor || localSettings.showNavigationBar,
+  showStatusBar: localSettings.showStatusBar,
+  showEditor: localSettings.showEditor,
+  showSidePreview: localSettings.showSidePreview && localSettings.showEditor,
+  showPreview: localSettings.showSidePreview || !localSettings.showEditor,
+  showSideBar: localSettings.showSideBar,
+  showExplorer: localSettings.showExplorer,
+}) {
+  styles.innerHeight = state.bodyHeight;
+  if (styles.showNavigationBar) {
+    styles.innerHeight -= constants.navigationBarHeight;
+  }
+  if (styles.showStatusBar) {
+    styles.innerHeight -= constants.statusBarHeight;
+  }
+
+  styles.innerWidth = state.bodyWidth;
+  if (styles.showSideBar) {
+    styles.innerWidth -= constants.sideBarWidth;
+  }
+  if (styles.showExplorer) {
+    styles.innerWidth -= constants.explorerWidth;
+  }
+
+  let doublePanelWidth = styles.innerWidth - constants.buttonBarWidth;
+  if (doublePanelWidth < editorMinWidth) {
+    doublePanelWidth = editorMinWidth;
+    styles.innerWidth = editorMinWidth + constants.buttonBarWidth;
+  }
+
+  if (styles.showSidePreview && doublePanelWidth / 2 < editorMinWidth) {
+    styles.showSidePreview = false;
+    styles.showPreview = false;
+    return computeStyles(state, localSettings, styles);
+  }
+
+  styles.fontSize = 18;
+  styles.textWidth = 990;
+  if (doublePanelWidth < 1120) {
+    styles.fontSize -= 1;
+    styles.textWidth = 910;
+  }
+  if (doublePanelWidth < 1040) {
+    styles.textWidth = 830;
+  }
+  styles.textWidth *= state.editorWidthFactor;
+  if (doublePanelWidth < styles.textWidth) {
+    styles.textWidth = doublePanelWidth;
+  }
+  if (styles.textWidth < 640) {
+    styles.fontSize -= 1;
+  }
+  styles.fontSize *= state.fontSizeFactor;
+
+  const bottomPadding = Math.floor(styles.innerHeight / 2);
+  const panelWidth = Math.floor(doublePanelWidth / 2);
+  styles.previewWidth = styles.showSidePreview ?
+    panelWidth :
+    styles.innerWidth;
+  const previewLeftPadding = Math.max(
+    Math.floor((styles.previewWidth - styles.textWidth) / 2), minPadding);
+  let previewRightPadding = previewLeftPadding;
+  if (!styles.showEditor && previewRightPadding < previewButtonWidth) {
+    previewRightPadding = previewButtonWidth;
+  }
+  styles.previewPadding = `${editorTopPadding}px ${previewRightPadding}px ${bottomPadding}px ${previewLeftPadding}px`;
+  styles.editorWidth = styles.showSidePreview ?
+    panelWidth :
+    doublePanelWidth;
+  const editorSidePadding = Math.max(
+    Math.floor((styles.editorWidth - styles.textWidth) / 2), minPadding);
+  styles.editorPadding = `${editorTopPadding}px ${editorSidePadding}px ${bottomPadding}px`;
+
+  styles.titleMaxWidth = styles.innerWidth - navigationBarSpaceWidth;
+  if (styles.showEditor) {
+    styles.titleMaxWidth -= navigationBarLeftWidth;
+  }
+  styles.titleMaxWidth = Math.min(styles.titleMaxWidth, maxTitleMaxWidth);
+  styles.titleMaxWidth = Math.max(styles.titleMaxWidth, minTitleMaxWidth);
+  return styles;
+}
+
 const setter = propertyName => (state, value) => {
   state[propertyName] = value;
 };
@@ -14,13 +105,6 @@ const setter = propertyName => (state, value) => {
 export default {
   namespaced: true,
   state: {
-    constants: {
-      explorerWidth: 250,
-      sideBarWidth: 280,
-      navigationBarHeight: 44,
-      buttonBarWidth: 30,
-      statusBarHeight: 20,
-    },
     editorWidthFactor: 1,
     fontSizeFactor: 1,
     bodyWidth: 0,
@@ -35,104 +119,10 @@ export default {
     },
   },
   getters: {
+    constants: () => constants,
     styles: (state, getters, rootState, rootGetters) => {
       const localSettings = rootGetters['data/localSettings'];
-      const styles = {
-        showNavigationBar: !localSettings.showEditor || localSettings.showNavigationBar,
-        showStatusBar: localSettings.showStatusBar,
-        showEditor: localSettings.showEditor,
-        showSidePreview: localSettings.showSidePreview && localSettings.showEditor,
-        showPreview: localSettings.showSidePreview || !localSettings.showEditor,
-        showSideBar: localSettings.showSideBar,
-        showExplorer: localSettings.showExplorer,
-      };
-
-      function computeStyles() {
-        styles.innerHeight = state.bodyHeight;
-        if (styles.showNavigationBar) {
-          styles.innerHeight -= state.constants.navigationBarHeight;
-        }
-        if (styles.showStatusBar) {
-          styles.innerHeight -= state.constants.statusBarHeight;
-        }
-
-        styles.innerWidth = state.bodyWidth;
-        if (styles.showSideBar) {
-          styles.innerWidth -= state.constants.sideBarWidth;
-        }
-        if (styles.showExplorer) {
-          styles.innerWidth -= state.constants.explorerWidth;
-        }
-
-        let doublePanelWidth = styles.innerWidth - state.constants.buttonBarWidth;
-        if (doublePanelWidth < editorMinWidth) {
-          if (styles.showSideBar) {
-            styles.showSideBar = false;
-            computeStyles();
-            return;
-          }
-          if (styles.showExplorer) {
-            styles.showExplorer = false;
-            computeStyles();
-            return;
-          }
-          doublePanelWidth = editorMinWidth;
-        }
-
-        if (styles.showSidePreview && doublePanelWidth / 2 < editorMinWidth) {
-          styles.showSidePreview = false;
-          styles.showPreview = false;
-          computeStyles();
-          return;
-        }
-
-        styles.fontSize = 18;
-        styles.textWidth = 990;
-        if (doublePanelWidth < 1120) {
-          styles.fontSize -= 1;
-          styles.textWidth = 910;
-        }
-        if (doublePanelWidth < 1040) {
-          styles.textWidth = 830;
-        }
-        styles.textWidth *= state.editorWidthFactor;
-        if (doublePanelWidth < styles.textWidth) {
-          styles.textWidth = doublePanelWidth;
-        }
-        if (styles.textWidth < 640) {
-          styles.fontSize -= 1;
-        }
-        styles.fontSize *= state.fontSizeFactor;
-
-        const bottomPadding = Math.floor(styles.innerHeight / 2);
-        const panelWidth = Math.floor(doublePanelWidth / 2);
-        styles.previewWidth = styles.showSidePreview ?
-          panelWidth :
-          styles.innerWidth;
-        const previewLeftPadding = Math.max(
-          Math.floor((styles.previewWidth - styles.textWidth) / 2), minPadding);
-        let previewRightPadding = previewLeftPadding;
-        if (!styles.showEditor && previewRightPadding < previewButtonWidth) {
-          previewRightPadding = previewButtonWidth;
-        }
-        styles.previewPadding = `${editorTopPadding}px ${previewRightPadding}px ${bottomPadding}px ${previewLeftPadding}px`;
-        styles.editorWidth = styles.showSidePreview ?
-          panelWidth :
-          doublePanelWidth;
-        const editorSidePadding = Math.max(
-          Math.floor((styles.editorWidth - styles.textWidth) / 2), minPadding);
-        styles.editorPadding = `${editorTopPadding}px ${editorSidePadding}px ${bottomPadding}px`;
-
-        styles.titleMaxWidth = styles.innerWidth - navigationBarSpaceWidth;
-        if (styles.showEditor) {
-          styles.titleMaxWidth -= navigationBarLeftWidth;
-        }
-        styles.titleMaxWidth = Math.min(styles.titleMaxWidth, maxTitleMaxWidth);
-        styles.titleMaxWidth = Math.max(styles.titleMaxWidth, minTitleMaxWidth);
-      }
-
-      computeStyles();
-      return styles;
+      return computeStyles(state, localSettings);
     },
   },
 };