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HTML

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HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

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Adding Classes

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. So you don't have access to higher-up elements like the <html> tag. If you want to add classes there that can affect the whole document, this is the place to do it.

About the <head>

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. If you need things in the <head> of the document, put that code here.

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Insecure Resource

The resource you are linking to is using the 'http' protocol, which may not work when the browser is using https.

CSS

About CSS Preprocessors

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

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

Vendor Prefixing

About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

We offer two popular choices: Autoprefixer (which processes your CSS server-side) and -prefix-free (which applies prefixes via a script, client-side).

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You can apply CSS to your Pen from any stylesheet on the web. Just put a URL to it here and we'll apply it, in the order you have them, before the CSS in the Pen itself.

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JavaScript

About JavaScript Preprocessors

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

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Babel includes JSX processing.

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If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.

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Packages

Add Packages

Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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Using packages here is powered by esm.sh, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ESM usage.

All packages are different, so refer to their docs for how they work.

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HTML 

              
                <canvas id="canvas" width="500" height="500" />

<script id="vertexShader" type="x-shader/x-vertex">
  #version 300 es

  in vec4 vertexPosition;

  void main() {
    gl_Position = vertexPosition;
  }
</script>

<script id="fragmentShader" type="x-shader/x-fragment">
  #version 300 es
  precision highp float;

  uniform vec2 canvasSize;
  uniform float time;
  out vec4 fragColor;

  void main() {
    vec2 coord = 2.*gl_FragCoord.xy/canvasSize.xy - 1.; // [-1,1]
    float scale = (sin(time) + 1.)/2.; // from 1 to 0
    coord /= scale; // from [-1,1] to [-infinity,infinity]
    if (abs(coord.x) < 1. && abs(coord.y) < 1.) {
      coord = (coord + 1.)/2.; // [0,1]
      fragColor = vec4(coord.x, coord.y, 1.-coord.x, 1);
    } else {
      fragColor = vec4(1,1,1,1);
    }
  }
</script>
!

CSS 

              
                body {
  text-align: center;
}
canvas {
  max-width: 100vw; 
  max-height: 100vh;
}
!

JS 

              
                // Requires a WebGL2-compatible browser: https://caniuse.com/?search=webgl2
// Confirm your compatibility: https://get.webgl.org/webgl2/
// Older versions of Safari (iOS/MacOS) may need to enable WebGL2 under "Experimental Features"

// More WebGL2 demos: https://codepen.io/collection/aMoEeq

const gl = canvas.getContext("webgl2");
if (!gl) throw "WebGL2 not supported";

function createShader(type, sourceCode) {
  const shader = gl.createShader(type);
  gl.shaderSource(shader, sourceCode.trim());
  gl.compileShader(shader);
  if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
    throw gl.getShaderInfoLog(shader);
  }
  return shader;
}

const program = gl.createProgram();
gl.attachShader(program, createShader(gl.VERTEX_SHADER, vertexShader.textContent));
gl.attachShader(program, createShader(gl.FRAGMENT_SHADER, fragmentShader.textContent));
gl.linkProgram(program);
if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
  throw gl.getProgramInfoLog(program);
}
gl.useProgram(program);

const vertices = [
  [-1, -1],
  [1, -1],
  [-1, 1],
  [1, 1],
];
gl.bindBuffer(gl.ARRAY_BUFFER, gl.createBuffer());
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices.flat()), gl.STATIC_DRAW);

const vertexPosition = gl.getAttribLocation(program, "vertexPosition");
gl.enableVertexAttribArray(vertexPosition);
gl.vertexAttribPointer(vertexPosition, vertices[0].length, gl.FLOAT, false, 0, 0);

gl.uniform2f(
  gl.getUniformLocation(program, 'canvasSize'),
  canvas.width, canvas.height
);
const timeUniform = gl.getUniformLocation(program, 'time');

function draw() {
  gl.uniform1f(timeUniform, performance.now() / 1000.);
  gl.drawArrays(gl.TRIANGLE_STRIP, 0, vertices.length);
  requestAnimationFrame(draw);
}
draw();
!
999px

Console