i want to modify the CSS, but I cant find the elements without the Developer tools option
Ctrl-shift-I is worked for me in 0.8.14. Is it also worked for you?
nope. not working
Hmm… just guessing, are you set ctrl+shift+i for other hotkey? set it for other hotkey function makes it can’t open developer tools.
If that is not the case, I’m sorry, I can’t help. I don’t know more than that. 
Try to discuss it in discord may help.
On mac is cmd-alt-i
yeah on my external keyboard the command to open the console in Obsidian.md is windows-alt-i