Fixed mode is not responsive for screen sizes smaller than 418px

Hello there, I have been given an assignment by my University to find an Open Source project, report a new issue and try to fix it. It's necessary for my assignment **that I interact with the project's community** so please respond to this message after you read it 🙏🏻

**The steps to reproduce the bug:**
To reproduce the problem you have to setup APlayer using "fixed mode":
```
const ap = new APlayer({
container: document.getElementById('aplayer'),
fixed: true, <-------
audio: [{
...
}]
});
```
Then, **AFTER the player has loaded up on the screen, resize the window to a size smaller than 418 pixels** as shown in this GIF I made:
While APlayer loads up correctly for any screen size if you reload the page, as you can see, APlayer does not resize responsively if you change the brower's size after the player has loaded up.

The expected behaviour of course would be that the player is **responsive for screen sizes smaller than 418px**. I tried fixing the issue on my browser using Dev Tools to excibit the desirable behaviour:

**Which versions of APlayer, and which browser / OS are affected by this issue?**
I observed this problem on **Windows** & the **Brave Browser** but this doesn't seem like a browser-specific or OS-specific problem.