version 2 maybe?

Makefile

@@ -4,7 +4,7 @@ DATADIR ?= $(PREFIX)/share
 CONFDIR = /etc
 
 install:
-	sed "s/%DATADIR%/\/usr\/share/" lightdm-mobile-greeter.py > lightdm-mobile-greeter
+	sed "s#%DATADIR%#$(DATADIR)#" lightdm-mobile-greeter.py > lightdm-mobile-greeter
 	install -Dm755 lightdm-mobile-greeter -t $(DESTDIR)$(BINDIR)
 	install -Dm644 style.css interface.ui -t $(DESTDIR)$(DATADIR)/lightdm-mobile-greeter
 	install -Dm644 lightdm-mobile-greeter.desktop -t $(DESTDIR)$(DATADIR)/xgreeters

interface.ui

@@ -17,13 +17,14 @@
                 <property name="orientation">vertical</property>
                 <property name="halign">center</property>
                 <property name="valign">center</property>
-                <property name="hexpand">True</property>
-                <property name="vexpand">True</property>
                 <property name="spacing">12</property>
                 <child>
                   <object class="GtkLabel" id="prompt_label">
                       <property name="visible">True</property>
                       <property name="label">prompt label</property>
+                      <style>
+                        <class name="prompt" />
+                      </style>
                   </object>
                 </child>
                 <child>
@@ -40,6 +41,9 @@
                     <property name="caps_lock_warning">False</property>
                     <property name="hexpand">True</property>
                     <property name="vexpand">True</property>
+                    <style>
+                      <class name="pin" />
+                    </style>
                   </object>
                 </child>
                 <child>
@@ -53,6 +57,7 @@
                     <property name="only_digits">True</property>
                     <property name="show_symbols">False</property>
                     <property name="right_action">delete_btn</property>
+                    <property name="left_action">settings_btn</property>
                     <property name="entry">pin_entry</property>
                     <style>
                       <class name="keypad"/>
@@ -60,26 +65,19 @@
                   </object>
                 </child>
                 <child>
-                  <object class="GtkBox">
+                  <object class="GtkButton">
                     <property name="visible">True</property>
-                    <child>
+                    <property name="label">Login</property>
-                      <object class="GtkButton">
+                    <signal name="clicked" handler="login_cb"/>
-                        <property name="visible">True</property>
+                    <style>
-                        <property name="label">Login</property>
+                      <class name="login_btn"/>
-                        <signal name="clicked" handler="login_cb"/>
+                    </style>
-                      </object>
-                      <packing>
-                        <property name="expand">False</property>
-                        <property name="fill">True</property>
-                        <property name="pack_type">end</property>
-                      </packing>
-                    </child>
                   </object>
                 </child>
                 <child>
                   <object class="GtkLabel" id="message_label">
                       <property name="visible">True</property>
-                      <property name="label">message label</property>
+                      <property name="label"></property>
                   </object>
                 </child>
               </object>
@@ -99,7 +97,25 @@
       <object class="GtkImage">
         <property name="visible">True</property>
         <property name="icon_name">edit-clear-symbolic</property>
+        <property name="icon_size">6</property>
       </object>
     </child>
   </object>
+  <object class="GtkButton" id="settings_btn">
+    <property name="visible">True</property>
+    <property name="can_focus">True</property>
+    <property name="focus-on-click">False</property>
+    <signal name="clicked" handler="de_popover"/>
+    <child>
+      <object class="GtkImage">
+        <property name="visible">True</property>
+        <property name="icon_name">applications-system-symbolic</property>
+        <property name="icon_size">6</property>
+      </object>
+    </child>
+  </object>
+  <object class="GtkPopover" id="de_select">
+    <property name="relative_to">settings_btn</property>
+    <property name="position">GTK_POS_RIGHT</property>
+  </object>
 </interface>

lightdm-mobile-greeter.py

@@ -20,9 +20,28 @@ class Handler:
         self.greeter.connect("show-prompt", self.show_prompt)
         self.pmpt_label = builder.get_object("prompt_label")
         self.msg_label = builder.get_object("message_label")
+        self.de_select = builder.get_object("de_select")
+        vbox = Gtk.Box(orientation=Gtk.Orientation.VERTICAL, visible=True)
+        self.de_select.add(vbox)
         self.greeter.connect_sync()
         self.conf = Config()
         self.greeter.authenticate(self.conf.user)
+        self.session = self.greeter.get_default_session_hint()
+        sessions = iter([(s.get_name(), s.get_key()) for s in LightDM.get_sessions()])
+        name, key = sessions.__next__()
+        first = Gtk.RadioButton.new_with_label(None, name)
+        first.connect("toggled", self.session_change, key)
+        vbox.add(first)
+        for name, key in sessions:
+            rb = Gtk.RadioButton.new_with_label_from_widget(first, name)
+            rb.connect("toggled", self.session_change, key)
+            vbox.add(rb)
+            if self.session == key:
+                rb.set_active(True)
+        vbox.show_all()
+
+    def session_change(self, rb, key):
+        self.session = key
 
     def on_destry(self, window):
         Gtk.main_quit()
@@ -39,7 +58,7 @@ class Handler:
 
     def auth_complete(self, greeter):
         if greeter.get_is_authenticated():
-            greeter.start_session_sync(None)
+            greeter.start_session_sync(self.session)
         else:
             greeter.authenticate(self.conf.user)
 
@@ -49,6 +68,9 @@ class Handler:
     def show_prompt(self, greeter, text, type):
         self.pmpt_label.set_text(text)
 
+    def de_popover(self, settings_btn):
+        self.de_select.popup()
+
 
 Handy.Keypad()
 builder: Gtk.Builder = Gtk.Builder.new_from_file(

style.css

@@ -5,21 +5,15 @@ window * {
     text-decoration: none;
 }
 
+button {
+    border: none;
+    border-radius: 20em;
+}
+
 window {
     background-color: black;
 }
 
-button {
-    border: 0;
-    background: none;
-    outline-style: dashed;
-    margin: 0;
-    border-width: 2px;
-    padding: 16px 36px;
-}
-.keypad button {
-    padding: 16px 16px;
-}
 label {
     font-weight: bold;
 }
@@ -32,3 +26,28 @@ button:active {
 button:active label {
     color: black;
 }
+
+hdykeypad > button label{
+   font-size: 5em;
+   font-weight: bold;
+   padding: 10px;
+}
+
+.login_btn > label {
+    font-size: 2em;
+    background-clip: padding-box;
+    padding: 0.5em;
+}
+
+.pin, .prompt {
+   font-size: 2em;
+}
+
+popover {
+    background-color: black;
+    font-size: 2em;
+}
+
+popover radiobutton {
+    padding: 1em;
+}