The report items that have explicitly set background in the report definition are not highlighted by the Search functionality of the viewer when their content matches the search.

Reproducible with Blazor Native Report Viewer.

Partially reproducible with HTML5 Viewer - the highlighted (when selecting the item in the Search list) class is applied but the shaded is not.

The workaround is to use the following styles on the page with the viewer:

<style>
    .trv-report-viewer-wrapper .trv-search-dialog-highlighted-result {
        background-color: rgba(0, 35, 102, 0.3);
        color: #fff;
        background-image: none;
    }

    .trv-report-viewer-wrapper .trv-search-dialog-shaded-result {
        background-color: rgba(255, 140, 0, 0.3);
    }
</style>