Tweak after testing with LightDM.

css/lightdm-uestibulum.css

@@ -1,52 +0,0 @@
-* { margin: 0; padding: 0; }
-
-body {
-  font-family: sans-serif
-}
-
-#bg {
-  position: fixed;
-  width: 100%;
-  display: block;
-  bottom: 0;
-  right: 0;
-  z-index: -1;
-}
-
-#power-panel {
-  color: white;
-  cursor: pointer;
-
-  background: rgba(8, 8, 8, 0.3);
-  box-shadow: 0px 0px 1em 1em (8, 8, 8, 0.3);
-  position: absolute;
-  bottom: 2em;
-  opacity: 0.5;
-  right: 2em;
-  transition: 1s;
-}
-
-#power-options {
-  border-radius: 10px;
-  padding: 1em;
-  transition: 1s;
-  display: none;
-}
-
-#power-panel.active #power-options {
-  display: block;
-}
-
-#power-panel.active #power-button { display: none; }
-
-#power-options ul { list-style: none; }
-
-#power-options li {
-  margin-bottom: 1em;
-  font-size: 200%;
-}
-
-#power-options li:last-child {
-  margin-bottom: 0;
-}
-

css/lightdm-uestibulum.scss

@@ -99,7 +99,7 @@ body {
     color: $colorFG;
     font-size: 1vw;
     margin-top: 0.5em;
-    //opacity: 0;
+    opacity: 0;
     transition: 0.5s;
     width: 20em;
 
@@ -146,8 +146,10 @@ body {
   &:hover { opacity: 1 };
 
   #sessions-list li { display: inline-block; }
+
 }
 
+
 #sessions { 
   cursor: pointer;
   display: inline-block;
@@ -172,6 +174,10 @@ body {
   #fail-msg { opacity: 1 !important; }
 }
 
+.lock-screen {
+  #session-panel { display: none !important; }
+}
+
 @keyframes throb {
   from { opacity: 1; }
   to { opacity: 0; }