Can't CSS some elements in a widget

I'm trying to personalize elements of a trending widget in extra.less but some elements refuses to be edited within data-widget-key
Less:

[data-widget-key="trendingHomeWidget"] {
    .block--messages .message, .block--messages .block-row {
        border-color: #303030;
    }
    .block--previews .block-body {
            gap: 0;
    }
}

But it works like this:
Less:

[data-template="forum_list"] {
    .block--messages .message, .block--messages .block-row {
        border-color...

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