vas element created in the html
var canvas = document.getElementById('my_dataviz2');

// Get the 'context'
var ctx = canvas.getContext('2d');

// Left: filled rectangle
ctx.fillStyle = '#69b3a2'; // rectangle color
ctx.fillRect(10, 10, 50, 50); // 4 arguments for the rect features: x, y, width and height

// Center: rectangle outline
ctx.strokeRect(100, 100, 80, 80);

// Right: rectangle with a cleared area
ctx.fillRect(200, 200, 120, 120);
ctx.clearRect(210, 170, 80, 80);

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