My better discord custom css for cluttred sidebar.

better_discord_custom.css

[class^="expandedFolderIconWrapper"]{
    box-sizing: border-box;
    border: 1.5px dashed red;
    background-color: aliceblue;
    border-top-left-radius: 6px !important;
    border-top-right-radius: 6px !important;
}

[class^="wrapper"][role="treeitem"], [class^="closedFolderIconWrapper"]{
    filter: grayscale(0.75) brightness(0.65) contrast(1.2) opacity(0.5);
}

[class^="expandedFolderBackground"]{
    background-color: aliceblue;
    filter: contrast(2) brightness(0.16);
    margin-left: -4px;
    margin-bottom: -4px;
    padding-left: 8px;
    border-radius: 6px !important;
}