When you have a lot of files to mark as viewed and you don't want to click them all...

clickFileViewedViaRegex.js

function clickFileViewedViaRegex(regex, markAsViewed = true) {
    document.querySelectorAll('.file').forEach((item) => {
        if (item.querySelector('.file-header a[title]').getAttribute('title').match(regex)) {
            var checkbox =  item.querySelector('.js-reviewed-checkbox');
            if (markAsViewed && !checkbox.checked) checkbox.click();
            if (!markAsViewed && checkbox.checked) checkbox.click();
        }
    });
}

// example
// clickFileViewedViaRegex(/my-folder\/[a-z-]+\.css/, true);