Use rem units to define off screen content

Using 10000px means content will be visible on screens with ultra-high
resolution (although I don't think they exist nor will exist anytime
soon).

Having screens in the future with a width of 1000rem is less likely,
since a line with 1000 characters would be pretty much impossible to
read.

app/assets/stylesheets/admin/table_actions.scss

@@ -10,7 +10,7 @@
 
     > :first-child {
       @include bottom-tooltip;
-      left: -10000px;
+      left: $off-screen-left;
       opacity: 0;
       transform: translateX(-50%);
       transition: opacity 0.3s, left 0s 0.3s;
@@ -28,7 +28,7 @@
     }
 
     &:not(:focus) > :first-child:hover {
-      left: -10000px;
+      left: $off-screen-left;
     }
 
     &::before {