Is option to make static width for background-image for :before?

My program adding to div a random message generated and pushed by JS to .message:before contains the default background image.png
If the message is long, the image is 50px wide, but if it is shorter, the image is flatter than it should be.
Is there any option to set one image size regardless of message size?

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-css -->

.message {
  display: flex;
  padding: 5px;
  margin: 5px 65px;
  height: min-content;
  min-width: 10px;
  max-width: 400px;
  background-color: rgb(98, 117, 180);
  border-radius: 20px;
}

.message::before {
  content: '';
  position: relative;
  top: -5px;
  right: 60px;
  width: 50px !important;
  height: 50px;
  background-image: url('default-avatar.png');
  /* for see result, will generate by js personalised for every user */
  background-position: center;
  background-repeat: no-repeat;
  background-size: 50px 50px;
  border-radius: 50%;
  z-index: 99;
}

<!-- language: lang-html -->

<div class="content">
  <div class="chatsContainer">
    <div id="chatList">
      /* here generated divs with messages */
    </div>
  </div>
</div>

<!-- end snippet -->

I deleted max-width from .message and then every image printing good, but I need to set message width shorter than 50% - paddings and margins to set div at left side of .chatList

You could position the image absolute to the message container. I commeted my changes in the code.

<!-- begin snippet: js hide: false console: true babel: null -->

<!-- language: lang-css -->

.message {
  position: relative; /* changed this */
  display: flex;
  padding: 5px;
  margin: 5px 65px;
  min-height: 70px; /* changed this */
  min-width: 10px;
  max-width: 400px;
  background-color: rgb(98, 117, 180);
  border-radius: 20px;
}

.message::before {
  content: '';
  position: absolute; /* changed this */
  top: -5px;
  left: -60px; /* changed this */
  width: 50px !important;
  height: 50px;
  background-image: url('https://upload.wikimedia.org/wikipedia/commons/thumb/9/93/Amateur-made_Na%27vi.jpg/440px-Amateur-made_Na%27vi.jpg');
  /* for see result, will generate by js personalised for every user */
  background-position: center;
  background-repeat: no-repeat;
  background-size: 50px 50px;
  border-radius: 50%;
  z-index: 99;
}

<!-- language: lang-html -->

<div class="content">
  <div class="chatsContainer">
    <div id="chatList">
      <div class="message">
        Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet. 
      </div>
      <div class="message">
        Lorem ipsum
      </div>
      <div class="message">
        Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua.
      </div>
    </div>
  </div>
</div>

<!-- end snippet -->

What I'm seeing is the opposite of what you describe. With a long message your image gets squished, and with a short message it is okay.

The reason for this is because your ::before is set to position: relative. This means it is included in the size calculation for the .message element. If you open your dev tools in the browser and inspect the .message element you should see something like this:

One way to resolve this is to use position: absolute on the ::before element as it will remove it from the flow of the document. You'll also need to set position: relative on the .message selector because absolutely positioned elements will work with the closest positioned ancestor.

After that, just change the right: 60px to left: -60px in the ::before selector and you should see a result like this:

Here's the css I used for your reference:

.message {
    display: flex;
    padding: 5px;
    margin: 5px 65px;
    height: min-content;
    min-width: 10px;
    max-width: 400px;
    background-color: rgb(98, 117, 180);
    border-radius: 20px;
    position: relative;
}

.message::before {
    content: '';
    position: absolute;
    top: -5px;
    left: -60px;
    width: 50px !important;
    height: 50px;
    background-image: url('avatar.jpg');
    background-position: center;
    background-repeat: no-repeat;
    background-size: 50px 50px;
    border-radius: 50%;
    z-index: 99;
}

For your reference: https://developer.mozilla.org/en-US/docs/Web/CSS/position

Cheers!