[FIX] web_editor: properly detect background color in toolbar

When a background color is applied on an ancestor, while it's visibly
there, `getComputedStyle` doesn't know. Because it did depend on it,
the toolbar showed the wrong color in these cases.
Eg: `<span style="background-color: red;"><b>a[]bc</b></span>` was
showing no background color.

task-2778416

X-original-commit: a125933b34500d51183bc5eb02a531fb3b293de5
Part-of: odoo/odoo#86930

addons/web_editor/static/lib/odoo-editor/src/OdooEditor.js

@@ -1445,7 +1445,14 @@ export class OdooEditor extends EventTarget {
                 if (hasGradient && !hasTextGradientClass) {
                     hiliteColor = backgroundImage;
                 } else {
-                    hiliteColor = computedStyle.backgroundColor;
+                    let ancestor = endContainer;
+                    while (ancestor && !hiliteColor) {
+                        hiliteColor = ancestor.style.backgroundColor;
+                        ancestor = ancestor.parentElement;
+                    }
+                    if (!hiliteColor) {
+                        hiliteColor = computedStyle.backgroundColor;
+                    }
                 }
             }
         }