How to make a certain part of the field as type in?

Card Design
11

It is probably possible, maybe with some regex, but it would require quite a more complex solution I’m afraid.

Maybe you could try the following workaround:

Front template:

{{Front}}

<div id="type">{{type:Back}}</div>
<div id="back" hidden>{{Back}}</div>

<script>
var typeElement = document.querySelector("#type");
var backElement = document.querySelector("#back");
var backContent = backElement.innerHTML;
var regex = /\btype_answer\b/;

if (!regex.test(backContent)) {
   typeElement.style.display = "none";
} 
</script>

<script>
  (() => {
   /**
   * Type-in-the-answer live feedback for Anki (vague variant)
   * @author Matthias Metelka | @kleinerpirat
   */
    const input = document.querySelector("#typeans");
    const answer = document.querySelector('.type_answer').innerText;
    if (input) {
      input.addEventListener("input", () => {
        input.classList.add("typed");
        input.classList.toggle(
          "goodsofar",
          input.value == answer.substring(0, input.value.length)
        );
        input.classList.toggle(
          "correct",
          input.value == answer
        );
      });
    }
  })();
</script>

Back template:

<span class="BackSide">

{{Front}}

<hr id=answer>

<div id="back">{{Back}}</div>

</span>

Styling section:

#typeans {
  color: black;
}
#typeans.typed {
  background-color: #ff9999;
}
#typeans.typed.goodsofar {
  background-color: #ffff7f;
}
#typeans.typed.correct {
  background-color: #99ff99;
}
.BackSide .type_answer {
  font-weight: bold; 
  color: blue;
}

Basically, instead of using Anki’s default code for evaluating type input, I inserted a slightly modified version of the code found in this topic to have instant type answer feedback.
I also removed most of the type_answer code from the Back template.
The purpose of the class BackSide and this CSS .BackSide .type_answer { font-weight: bold; color: blue; } is to highlight the content of the .type_answer span, to still have some sort of visual feedback.