Check out example codes for "css circle". It will help you in understanding the concepts better.

Code Example 1

#circle {
      width: 100px;
      height: 100px;
      background: red;
      border-radius: 50%
    }

Code Example 2

<svg xmlns="http://www.w3.org/2000/svg">
    <circle cx="50" cy="50" r="50" fill="red" />
</svg>

Code Example 3

.arrow-up {
  width: 0; 
  height: 0; 
  border-left: 5px solid transparent;
  border-right: 5px solid transparent;
  
  border-bottom: 5px solid black;
}

.arrow-down {
  width: 0; 
  height: 0; 
  border-left: 20px solid transparent;
  border-right: 20px solid transparent;
  
  border-top: 20px solid #f00;
}

.arrow-right {
  width: 0; 
  height: 0; 
  border-top: 60px solid transparent;
  border-bottom: 60px solid transparent;
  
  border-left: 60px solid green;
}

.arrow-left {
  width: 0; 
  height: 0; 
  border-top: 10px solid transparent;
  border-bottom: 10px solid transparent; 
  
  border-right:10px solid blue; 
}

Code Example 4

<!DOCTYPE html>
  <html>
  <head>
  <meta charset=utf-8 />
  <title>Draw a circle</title>
  </head>
  <body onload="draw();">
  <canvas id="circle" width="150" height="150"></canvas>
  </body>
  </html>

Code Example 5

function draw()
  {
var canvas = document.getElementById('circle');
if (canvas.getContext)
{
var ctx = canvas.getContext('2d'); 
var X = canvas.width / 2;
var Y = canvas.height / 2;
var R = 45;
ctx.beginPath();
ctx.arc(X, Y, R, 0, 2 * Math.PI, false);
ctx.lineWidth = 3;
ctx.strokeStyle = '#FF0000';
ctx.stroke();
}
}

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