[FIX] web_editor: missing toolbar-bottom arrow

When the floating toolbar is placed at the bottom of the selected text,
an arrow should be visible above the toolbar (pointing to the selected
text).
The CSS ruleset that makes such arrow visible was not being applied due
to an error in the CSS selector.

task-3347670

X-original-commit: 1a526b915d185e0b29bd3f9a3ff67df5178450d4
Part-of: odoo/odoo#130022

addons/web_editor/static/src/js/editor/odoo-editor/src/style.scss

@@ -130,7 +130,7 @@
     background: #222222;
     color: white;
 
-    .toolbar-bottom::before {
+    &.toolbar-bottom::before {
         content: '';
         position: absolute;
         width: 0;