diff --git a/src/client/application/application-main-window.vala b/src/client/application/application-main-window.vala
index 4c6d1038..b56079cf 100644
--- a/src/client/application/application-main-window.vala
+++ b/src/client/application/application-main-window.vala
@@ -317,9 +317,9 @@ public class Application.MainWindow :
     [GtkChild]
     private Gtk.Box main_layout;
     [GtkChild]
-    private Gtk.Paned folder_paned;
+    private Hdy.Leaflet main_leaflet;
     [GtkChild]
-    private Gtk.Paned conversations_paned;
+    private Hdy.Leaflet conversations_leaflet;
     [GtkChild]
     private Gtk.Box folder_box;
     [GtkChild]
@@ -520,7 +520,6 @@ public class Application.MainWindow :
         });
 
         setup_layout(application.config);
-        this.folder_paned.orientation = Gtk.Orientation.HORIZONTAL;
         this.folder_box.pack_start(status_bar, false, false);
 
         update_command_actions();
@@ -1249,8 +1248,9 @@ public class Application.MainWindow :
             on_conversation_view_added
         );
 
-        this.conversations_paned.pack2(this.conversation_viewer, true, false);
+        this.conversation_viewer.hexpand = true;
         this.conversation_size_group.add_widget(this.conversation_viewer);
+        this.main_leaflet.add_with_properties(this.conversation_viewer, "name", "conversation", null);
 
         // Main toolbar
         this.main_toolbar = new MainToolbar(config);
diff --git a/src/client/components/main-toolbar.vala b/src/client/components/main-toolbar.vala
index 6ea472a8..286546d5 100644
--- a/src/client/components/main-toolbar.vala
+++ b/src/client/components/main-toolbar.vala
@@ -6,7 +6,7 @@
 
 // Draws the main toolbar.
 [GtkTemplate (ui = "/org/gnome/Geary/main-toolbar.ui")]
-public class MainToolbar : Gtk.Box {
+public class MainToolbar : Hdy.Leaflet {
     // How wide the left pane should be. Auto-synced with our settings
     public int left_pane_width { get; set; }
     // Used to form the title of the folder header
@@ -97,7 +97,8 @@ public class MainToolbar : Gtk.Box {
     public void set_conversation_header(Gtk.HeaderBar header) {
         conversation_header.hide();
         this.header_group.add_gtk_header_bar(header);
-        pack_start(header, true, true);
+        header.hexpand = true;
+        add(header);
     }
 
     public void remove_conversation_header(Gtk.HeaderBar header) {
diff --git a/src/client/conversation-viewer/conversation-viewer.vala b/src/client/conversation-viewer/conversation-viewer.vala
index f04a1d26..eec5f6a4 100644
--- a/src/client/conversation-viewer/conversation-viewer.vala
+++ b/src/client/conversation-viewer/conversation-viewer.vala
@@ -68,6 +68,10 @@ public class ConversationViewer : Gtk.Stack, Geary.BaseInterface {
     public signal void conversation_removed(ConversationListBox list);
 
 
+    static construct {
+        set_css_name("geary-conversation-viewer");
+    }
+
     /**
      * Constructs a new conversation view instance.
      */
diff --git a/ui/application-main-window.ui b/ui/application-main-window.ui
index 872f31bd..f7bb884e 100644
--- a/ui/application-main-window.ui
+++ b/ui/application-main-window.ui
@@ -24,13 +24,18 @@
             <property name="can_focus">False</property>
             <property name="orientation">vertical</property>
             <child>
-              <object class="GtkPaned" id="conversations_paned">
+              <object class="HdyLeaflet" id="main_leaflet">
                 <property name="visible">True</property>
                 <property name="can_focus">True</property>
+                <property name="can_swipe_back">True</property>
+                <property name="transition_type">over</property>
                 <child>
-                  <object class="GtkPaned" id="folder_paned">
+                  <object class="HdyLeaflet" id="conversations_leaflet">
                     <property name="visible">True</property>
                     <property name="can_focus">True</property>
+                    <property name="hexpand_set">True</property>
+                    <property name="can_swipe_back">True</property>
+                    <property name="transition_type">over</property>
                     <child>
                       <object class="GtkBox" id="folder_box">
                         <property name="visible">True</property>
@@ -40,6 +45,7 @@
                           <object class="GtkFrame" id="folder_frame">
                             <property name="visible">True</property>
                             <property name="can_focus">False</property>
+                            <property name="vexpand">True</property>
                             <property name="label_xalign">0</property>
                             <property name="shadow_type">in</property>
                             <child>
@@ -55,15 +61,26 @@
                             </style>
                           </object>
                           <packing>
-                            <property name="expand">True</property>
                             <property name="fill">True</property>
                             <property name="position">0</property>
                           </packing>
                         </child>
                       </object>
                       <packing>
-                        <property name="resize">False</property>
-                        <property name="shrink">False</property>
+                        <property name="name">folder</property>
+                      </packing>
+                    </child>
+                    <child>
+                      <object class="GtkSeparator" id="folder_separator">
+                        <property name="visible">True</property>
+                        <property name="can_focus">False</property>
+                        <property name="orientation">vertical</property>
+                        <style>
+                          <class name="sidebar"/>
+                        </style>
+                      </object>
+                      <packing>
+                        <property name="navigatable">False</property>
                       </packing>
                     </child>
                     <child>
@@ -97,22 +114,27 @@
                         </child>
                       </object>
                       <packing>
-                        <property name="resize">True</property>
-                        <property name="shrink">False</property>
+                        <property name="name">conversations</property>
                       </packing>
                     </child>
+                  </object>
+                  <packing>
+                    <property name="name">conversations</property>
+                  </packing>
+                </child>
+                <child>
+                  <object class="GtkSeparator" id="conversations_separator">
+                    <property name="visible">True</property>
+                    <property name="can_focus">False</property>
+                    <property name="orientation">vertical</property>
                     <style>
                       <class name="geary-sidebar-pane-separator"/>
                     </style>
                   </object>
                   <packing>
-                    <property name="resize">False</property>
-                    <property name="shrink">False</property>
+                    <property name="navigatable">False</property>
                   </packing>
                 </child>
-                <child>
-                  <placeholder/>
-                </child>
               </object>
               <packing>
                 <property name="expand">True</property>
@@ -146,6 +168,9 @@
   </object>
   <object class="GtkSizeGroup" id="folder_separator_size_group">
     <property name="mode">horizontal</property>
+    <widgets>
+      <widget name="folder_separator"/>
+    </widgets>
   </object>
   <object class="GtkSizeGroup" id="conversations_size_group">
     <property name="mode">horizontal</property>
@@ -155,6 +180,9 @@
   </object>
   <object class="GtkSizeGroup" id="conversations_separator_size_group">
     <property name="mode">horizontal</property>
+    <widgets>
+      <widget name="conversations_separator"/>
+    </widgets>
   </object>
   <object class="GtkSizeGroup" id="conversation_size_group">
     <property name="mode">horizontal</property>
diff --git a/ui/geary.css b/ui/geary.css
index 0ddfab30..2d1d48c3 100644
--- a/ui/geary.css
+++ b/ui/geary.css
@@ -12,12 +12,23 @@
   border-left-width: 0;
   border-top-width: 0;
   border-right-width: 0;
+  min-width: 300px;
 }
 .geary-conversation-frame > border {
   border-left-width: 0;
   border-top-width: 0;
   border-right-width: 0;
+  min-width: 360px;
 }
+
+treeview.sidebar {
+  border: none;
+}
+
+geary-conversation-viewer {
+  min-width: 360px;
+}
+
 /* For 3-pane mode only */
 .geary-sidebar-pane-separator.vertical .conversation-frame > border {
   border-bottom-width: 0;
diff --git a/ui/main-toolbar.ui b/ui/main-toolbar.ui
index 732a01b9..441cd146 100644
--- a/ui/main-toolbar.ui
+++ b/ui/main-toolbar.ui
@@ -7,13 +7,18 @@
     <property name="can_focus">False</property>
     <property name="icon_name">mail-archive-symbolic</property>
   </object>
-  <template class="MainToolbar" parent="GtkBox">
+  <template class="MainToolbar" parent="HdyLeaflet">
     <property name="visible">True</property>
     <property name="can_focus">False</property>
+    <property name="can_swipe_back">True</property>
+    <property name="transition_type">over</property>
     <child>
-      <object class="GtkBox">
+      <object class="HdyLeaflet" id="conversations_leaflet">
         <property name="visible">True</property>
         <property name="can_focus">False</property>
+        <property name="can_swipe_back">True</property>
+        <property name="transition_type">over</property>
+        <property name="hexpand_set">True</property>
         <child>
           <object class="GtkHeaderBar" id="folder_header">
             <property name="visible">True</property>
@@ -41,6 +46,9 @@
               </packing>
             </child>
           </object>
+          <packing>
+            <property name="name">folder</property>
+          </packing>
         </child>
         <child>
           <object class="GtkSeparator" id="folder_separator">
@@ -52,15 +60,14 @@
             </style>
           </object>
           <packing>
-            <property name="expand">False</property>
-            <property name="fill">True</property>
-            <property name="position">1</property>
+            <property name="navigatable">False</property>
           </packing>
         </child>
         <child>
           <object class="GtkHeaderBar" id="conversations_header">
             <property name="visible">True</property>
             <property name="can_focus">False</property>
+            <property name="hexpand">True</property>
             <property name="show_close_button" bind-source="MainToolbar" bind-property="show_close_button" bind-flags="sync-create"/>
             <child>
               <object class="GtkButton" id="compose_new_message_button">
@@ -102,12 +109,13 @@
               </packing>
             </child>
           </object>
+          <packing>
+            <property name="name">conversations</property>
+          </packing>
         </child>
       </object>
       <packing>
-        <property name="expand">False</property>
-        <property name="fill">True</property>
-        <property name="position">0</property>
+        <property name="name">conversations</property>
       </packing>
     </child>
     <child>
@@ -120,15 +128,14 @@
         </style>
       </object>
       <packing>
-        <property name="expand">False</property>
-        <property name="fill">True</property>
-        <property name="position">1</property>
+        <property name="navigatable">False</property>
       </packing>
     </child>
     <child>
       <object class="GtkHeaderBar" id="conversation_header">
         <property name="visible">True</property>
         <property name="can_focus">False</property>
+        <property name="hexpand">True</property>
         <property name="show_close_button" bind-source="MainToolbar" bind-property="show_close_button" bind-flags="sync-create"/>
         <child>
           <object class="GtkBox" id="reply_forward_buttons">
@@ -362,9 +369,7 @@
         </child>
       </object>
       <packing>
-        <property name="expand">True</property>
-        <property name="fill">True</property>
-        <property name="position">2</property>
+        <property name="name">conversation</property>
       </packing>
     </child>
   </template>