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HTML

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Insecure Resource

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CSS

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CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

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Vendor Prefixing

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JavaScript

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JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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HTML 

              
                    <body>

        <div class="description">

            <p>Here is a demo of an image being revelaed by moving the cursor over the window.</p>

        </div> 

        <div class="container" id="imageExampleContainer" onmousemove="revealImage(); return false;">

            <div class="imageViewerContainer" id="imageViewer" ></div>

        </div>

   <body>
!

CSS 

              
                .description{
    margin: 2% auto 2% auto;  
}

.description p{
    font-family: "Helvetica Neue", Arial, Helvetica, sans-serif;
    font-size: 1.2em;
    text-align: center;
}

.container{
    width: 70vw;
    height: 80vh;

    touch-action: pan-x pan-y pinch-zoom;
  
    border: 1px solid black;

    margin: 2vh auto;

}

.imageViewerContainer{
    position: relative;  
}

.clipContainer{
    width: 50vw;
    height: 25vh;

    margin: 2% auto 2% auto;
}

.clipContainer iframe{
    margin-left: 14%;

    width: 1280px;
    height: 720px;
}

.emptySpace{
    width: 50%;
    height: 200vh;
}

.showSmallClipViewer{
    position: fixed;
    right: 0;
    bottom: 0;    
    width: 320px;
    height: 240px;
  
    border: 1px solid red;
}

.showSmallClipViewer iframe{
    width: 320px;
    height: 240px;

    margin: 0 auto;
}
!

JS 

              
                var xPos, yPos, xCord, yCord;

var grid, rect, client_X, client_Y; 

var imageReveal;

var windowScrollTop, bottomOfWindow, elemTop, elemBottom;

function displayViewer(){
/* Displays a small window for the image in the reveal image demo */
  
  imageReveal.style.display = "block";    
  grid.style.cursor = "none";
}

function getValues(){
 /* Gets the values for the selected process varibles */

  grid = document.getElementById("imageExampleContainer");           
            
  rect = grid.getBoundingClientRect();

  imageReveal = document.getElementById("imageViewer");
                     
  imageReveal.style.left = xPos + "px";
  imageReveal.style.top = yPos + "px";
  imageReveal.style.width = "15%";
  imageReveal.style.height = "15%";    
}

function getPositionValues(){   
/* Get the position of the cursor */

    xPos =  event.clientX - rect.left;
    yPos = event.clientY - rect.top;

}

function revealImage(){
/* Shows a small part of the image specified in the url */

    var callingID = 1;

    getValues(callingID);

    getPositionValues();  
 
    client_X = event.clientX;
    client_Y = event.clientY;    
  
    /* + 5 adds a small buffer */
  
    if(client_X >= rect.left && client_X <= (rect.right + 5) - (imageReveal.offsetWidth)){ 
      if(client_Y >= rect.top && client_Y <= (rect.bottom + 5) - (imageReveal.offsetHeight)){
                
            displayViewer(callingID);        
                                    
             xCord = xPos;
             yCord = yPos;
  
             imageReveal.style.backgroundImage = "url('https://wallpaperaccess.com/full/2068577.jpg')";
             imageReveal.style.backgroundPosition
             imageReveal.style.backgroundPosition = "-" + xCord + "px " + "-" + yCord + "px";
             imageReveal.style.transform = "scale(1)";   
             imageReveal.style.border = "1px solid red";             
                              
        }
        else{
            reset(callingID);
        }

    }    
    else{
        reset(callingID);
    }

}

function reset(){  
/* Stops moving the image in the reveal image demo.*/
 
    imageReveal.style = "none";
    grid.style.cursor = "default";       

}
!
999px

Console