Reports

In css-tricks they have this article about auto-growing inputs:
https://css-tricks.com/auto-growing-inputs-textareas/

The one i like has just a line of JS. I know you said 0 JS, but you dont have many options i think, and it's nothing to complicated.

label {
  display: inline-grid;
}

label::after {
  content: attr(data-value) ' ';
  visibility: hidden;
  white-space: pre-wrap;
}

<label>
  <input type="text" name="" value="" oninput="this.parentNode.dataset.value = this.value" size="1">
</label>

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