🐞 Add z-index for button tooltip.

[XP1]

Bug Report:

• Description: The z-index for ImprovedTube's button tooltip is missing.

• Steps to reproduce this: Put the metadata buttons onto the second row:

/* Expand metadata buttons. */
ytd-watch-metadata #above-the-fold > #top-row {
    display: block;
}

/* Adjust metadata buttons. */
ytd-watch-metadata #above-the-fold > #top-row #actions #menu > ytd-menu-renderer {
    justify-content: normal;
}

• Since when?: Unknown
• Browser: Chromium-based

YouTube's tooltip tp-yt-paper-tooltip element uses z-index: 1002;. I would suggest adding that to the .improvedtube-player-button:hover::after rule in /js&css/extension/www.youtube.com/styles.css:

https://github.com/code-charity/youtube/blob/master/js%26css/extension/www.youtube.com/styles.css#L676

/* Fix ImprovedTube tooltip. */
.improvedtube-player-button:hover::after {
    z-index: 1002;
}