However I can provide you with the styles which you can use on the obtained theme to make header image visible both on mobile and tablets (portrait view).
In this case the developers of 3rd party themes should implement some workaround for 3rd party plugins.
Like in your case- search plugin. In my head, it can be done as a javascript popup, which appears after you click some icon in the console where you can see the text area of the search, otherwise the text area won't fit in the console due to other console items. This will require some additional work to do and it won't be done for free of course, as this is individual request
To not show search on mobile - this can be done within a theme in the media queries for max-width of 480px
to make replies area to be of the same background color and add separator line
add these styles to base.css file
after line 6573, right before /*media queries*/
.ow_forum_topic_posts .ow_ipc { background-color: #152737; padding: 5px;}
.ow_forum_topic_posts .ow_ipc_info { border-bottom: 1px solid; }
enable dev mode, refresh, disable dev mode