Logseq for desktop is an Electron app, which is basically a browser app. Right-clicking to open developer tools doesn’t work, but you can use ctrl/cmd-shift-i to inspect the code with devtools.
If adding it to the inline html isn’t working, try adding the tweak to custom.css either targeting the .pill element or any .raw_html element, and consider the !important tag (ie, display:inline !important; if it still doesn’t work.