https://codepen.io/strangerintheq/details/dyRogLO

happybday.css

body {
    margin: 0; 
    overflow: hidden;
}

a {
    position: fixed;
    display: inline-block;
    margin-left: calc(50vw - 70px);
    font-size:20px;
    z-index:1;
    color: white;
}

happybday.js

let canvas = document.createElement('canvas');
canvas.style.background = '#000'
document.body.appendChild(canvas);
let gl = canvas.getContext("webgl", {preserveDrawingBuffer: true}); 

let clearPass = program({
    type: gl.TRIANGLES, 
    vertexSize: 2,
    vertices: [-1,3,-1,-1,3,-1], // full screen triangle
    shaders: [`
            attribute vec2 pt;
            void main(void) {x[
                gl_Position=vec4(pt, 0.0, 1.0);
            }`, `
            void main(void) {
                gl_FragColor=vec4(0.0, 0.0, 0.0, 0.05);
            }`]
});

let particles = program({
    type: gl.POINTS,
    vertexSize: 4,
    vertices: createVertices(),
    uniforms: {time: '1f', resolution: '2f'},
    shaders: [`
            uniform float time;
            uniform vec2 resolution;
            attribute vec4 pt;
            varying float i;
            void main() {
                float aspect = resolution.y/resolution.x;
                float t = smoothstep(0.0, 1.0, fract(time*0.3));
                t += mod(floor(time*0.3), 2.0);
                t *= 3.1415;
                i = fract(pt.x*pt.y*pt.z*pt.w);
                vec2 c = (pt.xy + pt.zw)/2.0;
                float a = atan(pt.y - c.y, pt.x - c.x);
                float r = length(vec2(pt.x - c.x, pt.y - c.y));
                r -= sin(t*3.)*0.005; 
                c += vec2(cos(a+t), sin(a+t)) * r;
                gl_Position = vec4(c.x*aspect, c.y, 0., 1.);
                gl_PointSize = 10.0;
            }`, `
            uniform float time;
            varying float i;
            float ch(vec2 uv) {
                float d = length(uv - 0.5);
                return smoothstep(0.2, 0.00, d);
            }
            void main() {
                float d = length(gl_PointCoord.xy-0.5);
                d = smoothstep(0.5, 0.00, d);
                gl_FragColor = vec4(
                    ch(gl_PointCoord.xy-0.25*sin(time+i)),
                    ch(gl_PointCoord.xy),
                    ch(gl_PointCoord.xy+0.25*sin(time+i)), 
                    0.01
                 );
            }`]
});

gl.enable(gl.BLEND);

requestAnimationFrame(function draw(t) {
    
    gl.blendFunc(gl.ONE, gl.ONE); // additive
    particles.bind();
    if (canvas.width != innerWidth || canvas.height !== innerHeight) {
        particles.uniforms.resolution([innerWidth, innerHeight]);
        gl.viewport(0, 0, canvas.width = innerWidth, canvas.height = innerHeight);
    }
    particles.uniforms.time([t/1000]);
    particles.draw();
    
    gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA); 
    clearPass.bind();
    clearPass.draw();
    
    requestAnimationFrame(draw);
    
});

function program(o) {
    let pid = gl.createProgram();
    let bufferId = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, bufferId);
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(o.vertices), gl.STATIC_DRAW);
    o.shaders.forEach((src, i) => {
        let id = gl.createShader(i?gl.FRAGMENT_SHADER:gl.VERTEX_SHADER);
        gl.shaderSource(id, 'precision highp float;\n'+src);
        gl.compileShader(id);
        var message = gl.getShaderInfoLog(id);
        gl.attachShader(pid, id);
        if (message.length > 0) {
            console.log(src.split('\n').map((str, i) => 
                ("" + (1 + i)).padStart(4, "0") + ": " + str).join('\n'));
            throw message;
        }
    });
    gl.linkProgram(pid);
    gl.useProgram(pid);
    o.uniforms && Object.keys(o.uniforms).forEach(uf => {
        let loc = gl.getUniformLocation(pid, uf), 
            f = gl[`uniform${o.uniforms[uf]}`];
        o.uniforms[uf] = v => f.call(gl, loc, ...v);
    });
    let pt = gl.getAttribLocation(pid, "pt");
    gl.enableVertexAttribArray(pt);
    o.draw = () => {
        gl.drawArrays(o.type, 0, o.vertices.length/o.vertexSize);
    }
    o.bind = () => {
        gl.useProgram(pid);
        gl.bindBuffer(gl.ARRAY_BUFFER, bufferId);
        gl.vertexAttribPointer(pt, o.vertexSize, gl.FLOAT, false, 0, 0); 
    }
    return o;
}

function createVertices() {
    let count = 2000;
    let vertices = [];
    let s = 500;
    let canvas = document.createElement('canvas');
    canvas.width = canvas.height = s;
    let ctx = canvas.getContext('2d');
    ctx.clearRect(0, 0, s, s);
    ctx.font = `bold ${s/5}px Arial`;
    ctx.fillStyle = "red";
    ctx.textBaseline = "middle";
    ctx.textAlign = "center";
    let mask = ["HAPPY", "BIRTHDAY"].map(text => {
        ctx.clearRect(0, 0, s, s);
        ctx.fillText(text, s/2, s/2);
        let data = ctx.getImageData(0, 0, s, s);
        return (x, y) => data.data[((y|0)*s+(x|0))*4];
    }); 
    while (vertices.length < count*4) {
        let x1 = s*Math.random();
        let y1 = s*Math.random();
        if (!mask[0](x1, y1))
            continue
        let x2 = s*Math.random();
        let y2 = s*Math.random();
        if (!mask[1](x2, y2)) 
            continue
        let r = Math.sqrt(Math.pow(x2 - x1, 2) + Math.pow(y2 - y1, 2))/2;
        if (r>s/6) 
            continue
        vertices.push(2*(x2/s-0.5), 2*(0.5-y2/s), 2*(x1/s-0.5), 2*(0.5-y1/s));
    }
    return vertices;
}