Zend certified PHP/Magento developer

ThunderBird 115 – How to Hide the Unified Toolbar with CSS?

The Unified Toolbar is of no use to me and I would life to turn it off.

I have tried messing the with Dev Tools and the userChrome file, just to confirm my userChrome file works, the following highlights folders on the left panel:

/* Thunderbird userChrome.css */

#folderTree li[data-server-type] > div.container {
    color: rgb(40, 134, 56) !important;
    background-color: rgb(255, 0, 200) !important;
 }
 #folderTree li[data-server-type] > div.container > span.name {
    font-weight: 1200 !important;
 }

Using the DevTools I was able to temporarily hide the Unified toolbar, I copied the style, pasted it into the userChrome file, the userChrome files total content is:

/* Thunderbird userChrome.css */
 #unifiedToolbar {
    flex: 1 1 auto;
    display: none;
    align-items: center;
    padding-block: var(--unified-toolbar-padding);
    min-width: 0;
    overflow: hidden;
 }

But when I reopen Thunderbird, the toolbar is still visible. What am I doing wrong?