ESPHOME WEB Server Theme doesnt stay put

I have ESPHOME running on my Raspberry Pi 4. All installed this week. I’ve made a simple ESP8266 project - working just fine - but when I set the theme to dark in the web server… and update the project or even refresh my PC browser (Windows 64 - Chrome - updated this week) it always defaults back to white.

Any thoughts as to why? On the RPI4 (did the same when running on the PC - not updated to latest ESPHOME) I’m using ESPhome 2023.2.4