This may or may not be relevant at some point, but when I use main_activities to display the general member activities, the font is different than the rest of the site, and it doesn't show the picture of the member (it shows an icon of the type of activity). Here's a modified version of templates/ACTIVITY.tpl that fixes the font issue and also shows the picture of the member for that particular activity. This should not overwrite the default templates/ACTIVITY.tpl, it should only be used as a custom template for your theme.
<style>
.activities_content {
    font-family: 'Open Sans','Segoe UI',Tahoma,Verdana,Arial,Helvetica,sans-serif;
}
</style>


<div class="activities_avatar_box">
    
    
        <img src="https://composr.app/uploads/auto_thumbs/zuI5Ow0lp0EFvd6MnQcj4L7AExTISi5ybG46PA7wHR4.png" />

    

    
</div>

<div class="activities_line">
    <div class="activity_time right">
        
    </div>

    

    <div class="activities_content">
        
        
        
            
            

            
            
                {MESSAGE}
            
        
    </div>
</div>