[FIX] website: adapt parallax extensions to 10.0 refactoring

The s_parallax snippet was refactored in 10.0 but this refactoring
broke some snippet extensions such as the s_parallax_slider.
This made the texts disappear once the snippet was resized.

addons/website/static/src/less/website.edit_mode.less

@@ -105,7 +105,7 @@ table.editorbar-panel {
 }
 
 // parallax dropzones are in conflict with outside of parallax dropzones
-.parallax > .oe_structure > .oe_drop_zone {
+.parallax .oe_structure > .oe_drop_zone {
     &:first-child {
         top: 16px;
     }

addons/website/static/src/less/website.snippets.less

@@ -393,8 +393,26 @@ div.carousel {
 
 .parallax {
     position: relative;
+
+    .oe_structure {
+        > :first-child {
+            margin-top: 32px;
+        }
+        > :last-child {
+            margin-bottom: 32px;
+        }
+    }
+}
+
+.s_parallax {
     min-height: 200px;
 
+    > .oe_structure {
+        display: inline-block;
+        width: 100%;
+        vertical-align: middle;
+    }
+
     &::before {
         content: "";
         display: inline-block;
@@ -403,17 +421,4 @@ div.carousel {
         height: 100%;
         vertical-align: middle;
     }
-
-    > .oe_structure {
-        display: inline-block;
-        width: 100%;
-        vertical-align: middle;
-
-        > :first-child {
-            margin-top: 32px;
-        }
-        > :last-child {
-            margin-bottom: 32px;
-        }
-    }
 }