<button class="b3 f">button</button>

<br>
<a class="b3 f">without href</a>

<br>
<a href="/does-href-break-border" class="b3 f">with href</a>

<script>
if (CSS.paintWorklet) {              CSS.paintWorklet.addModule('/t_afif/pen/abwBPPz.js');
} else {
  alert("Your browser cannot run this demo. Consider Chrome or Edge instead")
}
</script>

@property --border{
  syntax: '<length>';
  inherits: true;
  initial-value: 0;
}
@property --s{
  syntax: '<number>';
  inherits: true;
  initial-value: 0;
}

button, a {
  --border:4px;
  display: inline-block;
  text-decoration: none;
  padding:10px 30px;
  margin:5px 10px;
  font-size:25px;
  font-weight:bold;
  font-family: Arial;
  text-transform:uppercase;
  color:#00aaff;
  border:none;
  background:none;
  cursor:pointer;
  position:relative;
  transition:.5s;
  clip-path:polygon(var(--path));
}
button:before, a:before {
  content:"";
  position:absolute;
  z-index:-1;
  inset:0;
  -webkit-mask:paint(polygon-border);
  background:currentColor;
}
button:hover, a:hover {
  color:#ff00aa;
}
.f {
  background:linear-gradient(#00aaff 0 0) bottom/100% 0% no-repeat;
  transiton:.5s;
}
.f:before {
  background:#00aaff;
}
.f:hover {
  color:#fff;
  background-size:100% 100%;
}
.d {
  --dash:11,5;
}
.h {
  --s:5;
  --dash:11,var(--s);
  transition:--s .7s;
}
.h:hover {
  --s:0;
}

.b3 {  --path:20% 0%, 90% 0%, 100% 20%, 100% 50%, 80% 100%, 20% 100%, 10% 100%, 0% 70%, 0% 40%}

body {
  background:#f3f3f3;
}

registerPaint('polygon-border', class  {

  static get inputProperties() {
    return [
      '--path',
      '--border',
      '--dash'
    ]
  }
  
  paint(ctx, size, properties) {

    const points = properties.get('--path').toString().split(',');
    const b = parseFloat(properties.get('--border').value);
    const d = properties.get('--dash').toString().split(',');
    const w = size.width;
    const h = size.height;
    
    const cc = function(x,y) {
      var fx=0,fy=0;
      if (x.indexOf('calc') > -1) {
        var tmp = x.replace('calc(','').replace(')','');
        if (tmp.indexOf('+') > -1) {
          tmp = tmp.split('+');
          fx = (parseFloat(tmp[0])/100)*w + parseFloat(tmp[1]);
        } else {
          tmp = tmp.split('-');
          fx = (parseFloat(tmp[0])/100)*w - parseFloat(tmp[1]);
        }
      } else if (x.indexOf('%') > -1) {
        fx = (parseFloat(x)/100)*w;
      } else if(x.indexOf('px') > -1) {
        fx = parseFloat(x);
      }
      
      if (y.indexOf('calc') > -1) {
        var tmp = y.replace('calc(','').replace(')','');
        if (tmp.indexOf('+') > -1) {
          tmp = tmp.split('+');
          fy = (parseFloat(tmp[0])/100)*h + parseFloat(tmp[1]);
        } else {
          tmp = tmp.split('-');
          fy = (parseFloat(tmp[0])/100)*h - parseFloat(tmp[1]);
        }
      } else if (y.indexOf('%') > -1) {
        fy = (parseFloat(y)/100)*h;
      } else if(y.indexOf('px') > -1) {
        fy = parseFloat(y);
      }
      return [fx,fy];
    }
    
    var p = points[0].trim().split(/(?!\(.*)\s(?![^(]*?\))/g);
    p = cc(p[0],p[1]);
    ctx.beginPath();
    ctx.setLineDash(d);
    ctx.moveTo(p[0],p[1]);
    
    for (var i = 1; i < points.length; i++) {
      p = points[i].trim().split(/(?!\(.*)\s(?![^(]*?\))/g);
      p = cc(p[0],p[1]);
      ctx.lineTo(p[0],p[1]);
    }
    ctx.closePath();
    ctx.lineWidth = 2*b;
    ctx.strokeStyle = '#000';
    ctx.stroke();
  }

})