some css missing in RW 7 preview mode

the stacks.css file is imported into the index.html file with:

<link rel="stylesheet" type="text/css" media="all" href="rw_common/plugins/stacks/stacks.css">

however in RW 7 preview the rw_common directory does not exist. it only exists in preview in RW8+ so this path can't be found. in RW7 the common files are combined with the "files" directory and exported separately for each page's preview