use .transition helpers

less/topic.less

@@ -292,11 +292,7 @@
 			top: 0px;
 			left: -7px;
 
-			-webkit-transition: opacity 250ms ease, top 250ms ease;
+			.transition(~"opacity ease 250ms, top ease 250ms")
-			-moz-transition: opacity 250ms ease, top 250ms ease;
-			-ms-transition: opacity 250ms ease, top 250ms ease;
-			-o-transition: opacity 250ms ease, top 250ms ease;
-			transition: opacity 250ms ease, top 250ms ease;
 		}
 
 		&.replying::after {

modules/taskbar.less

@@ -6,11 +6,7 @@
 	-moz-opacity: 0.75;
 	opacity: 0.75;
 	margin-top: 0;
-	-webkit-transition: opacity 150ms ease-in;
+	.transition(.15s ease-in opacity);
-	   -moz-transition: opacity 150ms ease-in;
-	    -ms-transition: opacity 150ms ease-in;
-	     -o-transition: opacity 150ms ease-in;
-	        transition: opacity 150ms ease-in;
 
 	&[data-active="1"] {
 		display: block;