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HTML 

              
                <!-- Quick start template: https://codepen.io/pen/?template=ZEyrWNe -->

<canvas id="canvas"></canvas>
<div>
  <h1>Gloopy Border</h1>
  <p>A GLSL shader made with Inigo Quilez's 3D Perlin noise function.</p>
  <label for="thickness">Thickness</label>
  <input type="range" id="thickness" name="thickness" min="0" max="50" value="25" step="0.1">
  <label for="intensity">Intensity</label>
  <input type="range" id="intensity" name="intensity" min="0" max="10" value="5" step="0.1">
  <label for="noise">Noise</label>
  <input type="range" id="noise" name="noise" min="0" max="50" value="20" step="0.1">
</div>

<script id="vertexShader" type="x-shader/x-vertex">
  attribute vec4 position;

  void main() {
    gl_Position = vec4( position );
  }
</script>

<script id="fragmentShader" type="x-shader/x-fragment">
  #ifdef GL_FRAGMENT_PRECISION_HIGH
  precision highp float;
  #else
  precision mediump float;
  #endif

  uniform vec2 u_resolution;
  uniform float u_time;
  uniform vec2 u_mouse;
  uniform float u_thickness;
  uniform float u_intensity;
  uniform float u_noise;
  
  //3D Gradient Noise by Inigo Quilez - iq/2013
  //https://www.shadertoy.com/view/Xsl3Dl
  vec3 hash( vec3 p ) // replace this by something better
  {
    p = vec3( dot(p,vec3(127.1,311.7, 74.7)),
          dot(p,vec3(269.5,183.3,246.1)),
          dot(p,vec3(113.5,271.9,124.6)));

    return -1.0 + 2.0*fract(sin(p)*43758.5453123);
  }

  float noise( in vec3 p )
  {
    vec3 i = floor( p );
    vec3 f = fract( p );
	
	  vec3 u = f*f*(3.0-2.0*f);

    return mix( mix( mix( dot( hash( i + vec3(0.0,0.0,0.0) ), f - vec3(0.0,0.0,0.0) ), 
                          dot( hash( i + vec3(1.0,0.0,0.0) ), f - vec3(1.0,0.0,0.0) ), u.x),
                     mix( dot( hash( i + vec3(0.0,1.0,0.0) ), f - vec3(0.0,1.0,0.0) ), 
                          dot( hash( i + vec3(1.0,1.0,0.0) ), f - vec3(1.0,1.0,0.0) ), u.x), u.y),
                mix( mix( dot( hash( i + vec3(0.0,0.0,1.0) ), f - vec3(0.0,0.0,1.0) ), 
                          dot( hash( i + vec3(1.0,0.0,1.0) ), f - vec3(1.0,0.0,1.0) ), u.x),
                     mix( dot( hash( i + vec3(0.0,1.0,1.0) ), f - vec3(0.0,1.0,1.0) ), 
                          dot( hash( i + vec3(1.0,1.0,1.0) ), f - vec3(1.0,1.0,1.0) ), u.x), u.y), u.z );
  }

  void main() {
    float borderWidth = u_thickness;
    
    float halfWidth = u_resolution.x * 0.5;
    float halfHeight = u_resolution.y * 0.5;
    
    float xv = abs(gl_FragCoord.x - halfWidth) - halfWidth + borderWidth;
    float yv = abs(gl_FragCoord.y - halfHeight) - halfHeight + borderWidth;
    
    xv /= borderWidth;
    yv /= borderWidth;
    
    float r = max(yv, xv);
    
    vec2 uv = gl_FragCoord.xy / u_resolution;
    //Smoothly extend on the x axis without stretching the noise
    uv.x *= u_resolution.x/u_resolution.y;
    uv *= u_noise;
    float n = noise( vec3(uv.x, uv.y, u_time / 2.0));
    r += n;
    r *= u_intensity;
    
    gl_FragColor = vec4( 0.0, 0.0, 0.0, r );
  }
</script>
!

CSS 

              
                body {
 margin: 0;
}

div {
  margin: 80px;
}

p {
  font-size: 22px;
}

label {
  font-size: 22px;
  font-weight: bold;
  display: block;
}

input {
  display: block;
  margin-bottom: 10px;
  width: 100%;
  max-width: 300px;
}

canvas {
 position: fixed;
 pointer-events: none;
 top: 0;
 left: 0;
 width: 100vw;
 height: 100vh;
}
!

JS 

              
                // Following the twgl tiny tutorial, https://twgljs.org/
// Code adapted from https://github.com/greggman/twgl.js/blob/master/examples/tiny.html

const gl = document.getElementById("canvas").getContext("webgl");
const programInfo = twgl.createProgramInfo(gl, ["vertexShader", "fragmentShader"]);

const arrays = {
  position: [-1, -1, 0, 1, -1, 0, -1, 1, 0, -1, 1, 0, 1, -1, 0, 1, 1, 0],
};
const bufferInfo = twgl.createBufferInfoFromArrays(gl, arrays);

const thicknessSlider = document.getElementById("thickness");
const intensitySlider = document.getElementById("intensity");
const noiseSlider = document.getElementById("noise");

let mouseX = 0, mouseY = 0;

document.getElementById("canvas").addEventListener('mousemove', e => {
  mouseX = e.clientX;
  mouseY = e.clientY;
});


function render(time) {
  //Paints only 25% pixels in the screen space, 
  //Slightly lower resolution but much better performance!
  //See also: the zoom feature of https://glslsandbox.com/
  
  //twgl.resizeCanvasToDisplaySize(gl.canvas, 0.5); 
  
  //Paints 4x the number of pixels.
  //Very computationally expensive in full screen on desktop devices
  twgl.resizeCanvasToDisplaySize(gl.canvas, 0.5); 

  gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

  const uniforms = {
    u_time: (time) * 0.002,
    u_resolution: [gl.canvas.width, gl.canvas.height],
    u_mouse: [mouseX, mouseY],
    u_thickness: thicknessSlider.value,
    u_intensity: intensitySlider.value,
    u_noise: noiseSlider.value,
  };

  gl.useProgram(programInfo.program);
  twgl.setBuffersAndAttributes(gl, programInfo, bufferInfo);
  twgl.setUniforms(programInfo, uniforms);
  twgl.drawBufferInfo(gl, bufferInfo);

  requestAnimationFrame(render);
}
requestAnimationFrame(render);
!
999px

Console