JSFiddle - React, Tailwind, and code Playground

HTML

<table>
<tr>
<td>Number of Answers:</td>
<td>
<input type="text" name="numberAnswer" id="numberAnswerTxt" onkeypress="return isNumberKey(event)" onChange="getButtons()" >
</td>
</tr>
<tr>
<td>Answer</td>
<td>
<table>
<tr>
<td>
<input class="answerBtns" name="answerAName"     id="answerA"         type="button"      value="A"         onclick="javascript:btnclick(this);"/>
<input class="answerBtns" name="answerBName"    id="answerB"         type="button"   value="B"         onclick="javascript:btnclick(this);"/>
<input class="answerBtns" name="answerCName"     id="answerC"         type="button"      value="C"         onclick="javascript:btnclick(this);"/>
<input class="answerBtns" name="answerDName"     id="answerD"         type="button"      value="D"         onclick="javascript:btnclick(this);"/>
<input class="answerBtns" name="answerEName"     id="answerE"         type="button"   value="E"         onclick="javascript:btnclick(this);"/>
<input class="answerBtns" name="answerFName"     id="answerF"         type="button"      value="F"         onclick="javascript:btnclick(this);"/>
<input class="answerBtns" name="answerGName"    id="answerG"         type="button"   value="G"         onclick="javascript:btnclick(this);"/>
</td>
</tr>
<tr>
<td>
<input class="answerBtns" name="answerHName"     id="answerH"         type="button"      value="H"         onclick="javascript:btnclick(this);"/>
<input class="answerBtns" name="answerIName"     id="answerI"         type="button"      value="I"         onclick="javascript:btnclick(this);"/>
<input class="answerBtns" name="answerJName"     id="answerJ"         type="button"   value="J"         onclick="javascript:btnclick(this);"/>
<input class="answerBtns" name="answerKName"     id="answerK"         type="button"      value="K"         onclick="javascript:btnclick(this);"/>
<input class="answerBtns" name="answerLName"    id="answerL"         type="button"   value="L"         onclick="javascript:btnclick(this);"/>
<input...

CSS

.answerBtns{
    background-color: #ffffff;
    border: #666666 1px solid;
    color: black;
    font-weight:bold;
    }
    
.answerBtnsOff{
    background-color: #ffffff;
    border: #666666 1px solid;
    color: black;
    font-weight:bold;
 
}
 
.answerBtnsOn{
    background-color: red;
    border: #666666 1px solid;
    color: #ffffff;
    font-weight:bold;
}

JavaScript

function getButtons() {
    for(var i = 65; i <= 90; i++) { // iterate over character codes for A to Z
        var letter = String.fromCharCode(i);
        document.getElementById("answer" + letter).className = "answerBtnsOff";
    }
    document.getElementById("answerTrue").className = "answerBtnsOff";
    document.getElementById("answerFalse").className = "answerBtnsOff";
    document.getElementById("answerYes").className = "answerBtnsOff";
    document.getElementById("answerNo").className = "answerBtnsOff";

    
    // code above makes sure all buttons start off with class answerBtnsOff, (so all button are white).
}

var currenttotal = 0;

function btnclick(btn) {
    if (document.getElementById("numberAnswerTxt").value == "") {
        alert('You must first enter in the number of answers you require in the textbox above');
        return false;
        
        //if text box empty then send alert
        
    }
    if (btn.className == "answerBtnsOn") {
        console.log(2);
        btn.className = "answerBtnsOff";
        currenttotal--;
        return false;
        
        //if a button is already selected (in other words "answerBtnsOn), then turn it off if clicked on
        
    }
    console.log(currenttotal);
    if (document.getElementById("numberAnswerTxt").value == currenttotal) {
        alert('You are not allowed beyond the limit of the number of answers you require, deselect other button');
        return false;
    }
    if (btn.className == "answerBtnsOff") {
        btn.className = "answerBtnsOn";
        currenttotal++;
        console.log(1);
        return false;
        
         //if a button is not selected (in other words "answerBtnsOff), then turn it on if clicked on 
        
    }

}