Bug 1095826 - [RTL][Video] Thumbnail images do not appear

I don't have much experience with display:flex, but it seems to me that you are not making much use of it. The align-items:stretch may actually be doing something helpful here, but you might actually be able to just do display:inline and have it work as well.  Since you're using calc() in the .details element instead of making that flexible I'm not sure you need this.