Fix sticker picker height

Fixes https://github.com/vector-im/element-web/issues/15152

res/css/views/rooms/_Stickers.scss

@@ -7,7 +7,8 @@
     height: 300px;
 }
 
-#mx_persistedElement_stickerPicker .mx_AppTileFullWidth {
+#mx_persistedElement_stickerPicker {
+    .mx_AppTileFullWidth {
         height: unset;
         box-sizing: border-box;
         border-left: none;
@@ -15,6 +16,12 @@
         border-bottom: none;
     }
 
+    iframe {
+        // Sticker picker depends on the fixed height previously used for all tiles
+        height: 273px;
+    }
+}
+
 .mx_Stickers_contentPlaceholder {
     display: flex;
     flex-grow: 1;