How do I make a chrome extension appear in the left side of the website?

I was searching many different website to see how I can position my HTML popup into the left side of the website, but many of them didn't work. My popup was stuck in the default element, such as when you create a normal popup and a window appears with a arrow above it. Is there any way to make the popup appear hovering the website while its on the left side of the screen?

body {
    width: 100%;
    height: 100%;
}

#popupContainer{
    background-color: blue;
    width: 200px;
    height: 100px;
    position: left;
}

<div id="popupContainer">
    <p>Popup content</p>
</div>