JSFiddle - React, Tailwind, and code Playground

HTML

<div name="mv" style="position:absolute; top:15%; left:0px; height:59%; width:30%; border:medium solid #FF7750;">
<p align="center" style="margin-left:5mm; font-weight:bold;">
Hier die Startzahlen eingeben!
</p>
<!-- Bereich 1 -->
<div style="position:absolute; top:10mm; left:7mm; height:24mm; width:27mm; background-color:#FF7750;">
<form>
<input id="Z1" type="text" class="kfeld1">
<input id="Z2" type="text" class="kfeld1">
<input id="Z3" type="text" class="kfeld1"><br>
<input id="Z4" type="text" class="kfeld1">
<input id="Z5" type="text" class="kfeld1">
<input id="Z6" type="text" class="kfeld1"><br>
<input id="Z7" type="text" class="kfeld1">
<input id="Z8" type="text" class="kfeld1">
<input id="Z9" type="text" class="kfeld1">
</form>
</div>
</div>

<div name="B2" align="center" style="position:absolute ; top:100px ; left:350px ;
background-color:#FF7750; height:20%; width:20%;">
<button type="button" id="Bu2" name="Bu2" value="Text" style="width:50px ; position:relative; top:40" >
<p>
Test
</p>
</button>
</div>

CSS

input.kfeld1 {position:relative; left:2mm; top:2mm; width:5mm; text-align:center; font-weight:bold;}

JavaScript

function anzeigen() {
    for(i = 1; i <= 9; i++)
    {
        var zaehler = "Z" + i ;
        document.getElementById(zaehler).value = i;
    }
}

document.getElementById("Bu2").addEventListener("click", anzeigen, false);