JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">

      

      <div class="main-content">

        <div class="header">
          <button class="add-row" onclick="addRow()">Add Row +</button>
          <button class="add-column" onclick="addCol()">Add Column +</button>
        </div>

        <div class="content-box" id="contentBox">

          <p>
          Click add row to add row, to add column - > click add column and select any added row
          </p>
        </div>

      </div>

    </div>

CSS

* {
	box-sizing: border-box;
}

.wrapper {
	float: left;
	width: 100%;
	height: 100vh;
}

body {
	padding: 0;
	margin: 0;
	position: relative;
}

.sidebar {
	float: left;
	width: 300px;
	background: #03A9F4;
	height: 100%;
	padding: 10px;
}

.main-content {
	float: left;
	width: 100%;
	height: 100%;
	background: #fafafa;
}

.each-draggable-item {
	width: 100%;
	height: 40px;
	padding: 0 10px;
	display: flex;
	align-items: center;
	border: 1px solid #ccc;
	background: white;
	margin-bottom: 10px;
	border-radius: 6px;
}


.header {
	height: 60px;
	display: flex;
	align-items: center;
	justify-content: flex-end;
	padding: 0 20px;
}

.content-box {
	width: 100%;
	height: calc(100% - 60px);
	padding: 15px;
}


button {
	background: #000;
	border: 0;
	padding: 0 20px;
	height: 40px;
	margin-left: 10px;
	font-weight: 600;
	color: white;
	cursor: pointer;
}

.row-block {
	width: 100%;
	border: 2px dashed #848484;
	padding: 20px;
	display: -webkit-box;
	display: -ms-flexbox;
	display: flex;
	-ms-flex-wrap: wrap;
	flex-wrap: wrap;
	margin-bottom: 20px;

}

.row-block:hover {
	border-color: #2654d1;
}

.column-block {
	position: relative;
	width: 100%;
	min-height: 1px;
	padding-right: 10px;
	padding-left: 10px;
	margin: 0 10px;
	-ms-flex-preferred-size: 0;
	flex-basis: 0;
	-webkit-box-flex: 1;
	-ms-flex-positive: 1;
	flex-grow: 1;
	max-width: 100%;
	border: 2px dashed #848484;

	background-color: #dedede;
	padding: 20px;
}

/* .column-inner {
  border: 2px dashed #848484;
  padding: 20px;
  min-height: 200px;
} */
.column-block:first-child {
	margin-left: 0;
}

.column-block:last-child {
	margin-right: 0;
}

.row-block .each-draggable-item {
	position: relative;
	width: 100%;
	min-height: 1px;
	padding-right: 10px;
	padding-left: 10px;
	-ms-flex-preferred-size: 0;
	flex-basis: 0;
	-webkit-box-flex: 1;
	-ms-flex-positive: 1;
	flex-grow: 1;
	max-width: 100%;
	margin-bottom: 0;
}

.gu-mirror {
	cursor: grabbing;
}

.container .ex-moved {
	background-color:...

JavaScript

// Row Addition
var i=0;
let newColNode = null;

function addRow() {    
    const row = document.createElement('div');
    row.className = 'row-block';
    row.id = "b" + ++i;
    document.getElementById('contentBox').appendChild(row);
    row.addEventListener('click', function (event) {
        if(newColNode != null)
        row.appendChild(newColNode);
        newColNode = null
    });
    row.addEventListener('dragover', dragOver); 
    row.addEventListener('dragenter', dragEnter); 
    row.addEventListener('dragleave', dragLeave);
    row.addEventListener('drop', Drop);
}

// Row Addition

function addCol() {
    const col = document.createElement('p');
    col.className = 'column-block';
    col.setAttribute('draggable', true);
    col.textContent = `Column`;
    newColNode = col;
    col.addEventListener('dragstart', dragStart); 
    col.addEventListener('dragend', dragEnd); 
}

// drag and drop

var p = document.getElementsByTagName('p');
var choice = document.getElementsByClassName('row-block');
var dragItem = null;

for (var i of p) {
    i.addEventListener('dragstart', dragStart);
    i.addEventListener('dragend', dragEnd);
}

function dragStart() {
    dragItem = this;
    setTimeout=(()=>this.style.display = "none", 0)
}

function dragEnd() {
    setTimeout=(()=>this.style.display = "none", 0)
    dragItem = null;
}

for(j of choice){
    j.addEventListener('dragover', dragOver); 
    j.addEventListener('dragenter', dragEnter); 
    j.addEventListener('dragleave', dragLeave);
    j.addEventListener('drop', Drop);
}

function Drop(){
    this.append(dragItem);
}

function dragOver(e){ 
    e.preventDefault();
}

function dragEnter(e){
    e.preventDefault();
}

function dragLeave(){
    // this.style.borderColor = "none";
}