Canvas drawing color transparent – Blancer.com Tutorials and projects

I don’t want to see the circles and the color should be a little transparent. And if I draw again, it shouldn’t be so transparent anymore.How can i do?
Here is my code.

window.addEventListener('load', ()=>{
        
    resize(); 
    document.addEventListener('mousedown', startPainting);
    document.addEventListener('mouseup', stopPainting);
    document.addEventListener('mousemove', sketch);
    window.addEventListener('resize', resize);
});
    
const canvas = document.querySelector('#canvas');
   
const ctx = canvas.getContext('2d');
    
function resize(){
  ctx.canvas.width = window.innerWidth;
  ctx.canvas.height = window.innerHeight;
}
    
let coord = {x:0 , y:0}; 
   
let paint = false;
    
function getPosition(event){
  coord.x = event.clientX - canvas.offsetLeft;
  coord.y = event.clientY - canvas.offsetTop;
}
  
function startPainting(event){
  paint = true;
  getPosition(event);
}
function stopPainting(){
  paint = false;
}
    
function sketch(event){
  if (!paint) return;
  ctx.beginPath();
    
  ctx.lineWidth = 100;
   
  ctx.lineCap = 'round';
    
  ctx.globalAlpha = 0.5;
  ctx.strokeStyle = 'rgba(255, 0, 0, 0.5)';
      
  ctx.moveTo(coord.x, coord.y);
   
  getPosition(event);
  
  ctx.lineTo(coord.x , coord.y);
   
  ctx.stroke();
}

.content {
  position: relative;
}

.something {
  position: absolute;
}

#canvas {
  position: absolute;
  user-select: none;
}

<body>
    <div class="content">
           <div class="something">
            test
          </div>
          <canvas id="canvas"></canvas>
    </div>
</body>

Please help me find the solution. I searched on google but couldn’t find a solution.
I want use like highlighter. Thanks if you can help me.

https://jsfiddle.net/epmo9buy/