@ryanbreed Thank you, I didn't know this. But I'm not comfortable with this solution.
Opera browser's UI is the best in my opinion and I expect it to be perfect.

Operating system: Windows 10

Before the update:
If we had lots of opened tabs we could still see the "X" button when we hover over a tab.

After the update:
But after the update, it doesn't show the "X" button when there are lots of open tabs even we hover over a tab.