Hi Amanda
I am somewhat unsure of what piece of inromation you are missing? Sure there are no videos, but creating custom system styles is a rather advanced topic, often (but not at all always) done by service providers. Note that you do not have to use the GUI in the administration, especially if you have experience in web-dev in might be easier for you to just hover over to the How-To 2 section, where you can read up on how to create skins manually. For your questions regarding System Styles and Sub Styles:
System Styles: Create own Skins for the complete installation (with a custom CSS). Note that you can also exchange the html templates.
Sub Styles: Create own Skins for a specific parts of your installation (with a custom CSS just active for e.g. a specific folder of you installation).
Since you have experience with Web Dev, probably best: First try to create a small first skin according to the "How-To 2" manually section and make some minor changes to just check if all works as expected. From there make the changes bigger. If interested you can also checkout our skin (University of Bern) to just have a template on how things could look. Note that this is no "How To" example, just an example ;-). Here you go: https://github.com/iLUB/ILIAS-Skin/tree/ilias6
I am somewhat unsure of what piece of inromation you are missing? Sure there are no videos, but creating custom system styles is a rather advanced topic, often (but not at all always) done by service providers. Note that you do not have to use the GUI in the administration, especially if you have experience in web-dev in might be easier for you to just hover over to the How-To 2 section, where you can read up on how to create skins manually. For your questions regarding System Styles and Sub Styles:
System Styles: Create own Skins for the complete installation (with a custom CSS). Note that you can also exchange the html templates.
Sub Styles: Create own Skins for a specific parts of your installation (with a custom CSS just active for e.g. a specific folder of you installation).
Since you have experience with Web Dev, probably best: First try to create a small first skin according to the "How-To 2" manually section and make some minor changes to just check if all works as expected. From there make the changes bigger. If interested you can also checkout our skin (University of Bern) to just have a template on how things could look. Note that this is no "How To" example, just an example ;-). Here you go: https://github.com/iLUB/ILIAS-Skin/tree/ilias6