Hello Sophie,
Please find my response below.
Q- how do I check the skins repository ie is it a directory on the server?
Q- where is the thtmld styles directory?
Q- where do I look for these IE compatible css files for skin nova?
A - You can refer skin workbench, spro path given below. Here you can see the .css files for specific IE version and also other related information.
Customer Relationship Management -> UI Framework -> UI Framework Definition -> Skins and Icons -> Access Skin Workbench
Q- SICF service /default_host/sap/bc/bsp/sap/thtmlb_styles is active (but there is no "sap_skin"s/nova" underneath it???
A - Apologies, this was a typo error. All skins are tagged under single service.
My questions to understand if this issue is local to one user/machine or global across many users:
I would like know if this issue faced by all users?
Have you tried changing IE browser?
Please refer more information on below links:
Common Issues with IE 11 Browser - CRM - SCN Wiki
Thanks,
Kapil