The position of the elements do not remain the same compared to their previous placed position using getBoundingClientRect

I drag and drop some elements on a div and upload the content . Before uploading I calculate the dropped element top,left positions , so that the top,left positions can be used to place the elements exactly at the same place when they are rendered on a different screen. But the issue is the elements are placed in a slightly different position compared to their initial placed position.

HTML Before Uploading

<div id="toget"
     class="dropzone"
     [ngStyle]="{'width':'100%',
                 'background-image': 'url('+urlFloorZoneIn+')',
                 'background-repeat': 'no-repeat',
                 'background-position': 'center',
                 'background-size': '100% 100%',
                 'border':'1px solid black',
                 'height':'340px',
                 'position': 'relative'}">

    <div class="box"
         *ngFor="let existingZone of existingDroppedItemZoneIn"
         [ngStyle] = "{'position': 'absolute' , 
                       'top.%':existingZone.spans[1], 
                       'left.%':existingZone.spans[0]}" >
        
        <span></span>
        <span></span>
    </div>

</div>

CSS

.box {
  width: 10%;
  height: 10%;
  background: rgba(254, 249, 247, 1);
  border: 1.5px solid #e24301;
  margin: 5px;
  line-height: 100px;
  text-align: center;
  font-size: 0.8rem;
}

.dropzone {
  padding: 20px;
  margin: 20px 0;
  background: lightgray;
  min-height: 200px;
  border: 1px solid black;
 }

Before rendering I get the top,left values of the above uploaded HTML content and apply the background-image, top, left values to render the below content

<ul>
    <li #allFloors
       *ngFor="let floor of buildings.floors"
       [ngStyle]="{'width': singleFloorFlagStyle ?'40%':'100%',
                   'background-image': 'url('+floor.urlFloorZoneIn+')', 
                   'background-repeat': 'no-repeat',
                   'background-position': 'center',
                   'background-size': '100% 100%',
                   'border':'1px solid black',
                   'height': singleFloorFlagStyle ? '340px' : '700px', 
                   'position': 'relative', 'max-width': '80%'}"
                   [ngClass]="{'width':'80% !important'}">

            <span (click)="loadFloorInfo(floor._id)"></span>
            <div class="fs-heatmap-wrapper__content__box"
                *ngFor="let existingZone of floor.droppeditem"
                [ngStyle]="{'position':'absolute',
                            'top.%': existingZone.spans[1],
                            'left.%': existingZone.spans[0]}">

                
             </div>      
    </li>
</ul>

CSS

.fs-heatmap-wrapper {
display: grid;
*min-height: 800px;
&__content {
    padding: 70px 40px 0;
    min-height: 300px;
    ul {
        margin: 0;
        padding: 0;
        display: flex;
        flex-wrap: wrap;
        justify-content: center;
        li {
            list-style: none;
            min-width: 48%;
            margin: 12px;
            margin-bottom: 2.5%;
            span {
                cursor: pointer;
                background: #fff;
                text-align: left;
                font-weight: 800;
                font-size: 0.9rem;
                letter-spacing: 0.05rem;
                position: relative;
                top: -30px;
            }
        }
    }

&__box{
width: 100px;       
height: 100px;      
background: rgba(254, 249, 247, 1);     
border: 1.5px solid #e24301;        
margin: 5px;        
line-height: 100px;     
text-align: center;     
font-size: 0.8rem;

    }
  }        
}

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