Have to click twice to switch from light to dark mode when my browser theme is dark

### Steps to reproduce

1. Set `"default_theme": "light"` in [config.json](https://uplink.mit.edu/config.json)
2. **Set your device or browser's theme to dark (instructions are platform-dependent)**
2. Log in with a brand new account
4. Click on your profile picture
5. Click on the change theme icon

Edit: This doesn't require a brand new account, just a brand new session.

### Outcome

#### What did you expect?

Theme changes from light to dark

#### What happened instead?

Theme stays light, and the tooltip says "switch to light mode" when I am already in light mode. I have to click it another time to switch to dark theme and only then does it act as a "toggle theme" button.

See screen recording in next comment.

### Operating system

Windows and Linux

### Browser information

Firefox 116.0

### URL for webapp

matrix.mit.edu (not public)

### Application version

Element version: 1.11.39 Olm version: 3.2.14

Can reproduce on develop branch too

### Homeserver

matrix-synapse-py3 1.90.0+jammy1

### Will you send logs?

Yes