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CSS

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CSS Base

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JavaScript

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HTML 

              
                .box
  h1.intro Fork me on GitHub
    small *animated* corner style generator

  form#corner-opts
    h2 options:
    dl
      dt
        label(for="opts_pos") position
      dd
        table
          tr
            td
              label
                input(type="radio", name="opts_pos", value="+-")
                | top-left
            td
              label
                input(type="radio", name="opts_pos", value="++", checked)
                | top-right
          tr
            td
              label
                input(type="radio", name="opts_pos", value="--")
                | bottom-left
            td
              label
                input(type="radio", name="opts_pos", value="-+")
                | bottom-right

      dt
        label(for="color") color
        small  /cat/
      dd
        input#color(type="color", name="color", value="#ffffff", required)
      dt
        label(for="fill") fill color
        small  /background-color/
      dd
        input#fill(type="color", name="fill", value="#000000", required)
      dt
        label(for="url") url
        small  /link/
      dd
        input#url(type="url", name="url", value="###", required)
      dt
        label(for="size") size
        small  /px/
      dd
        input#size(type="number", name="size", min="0", step="5", value="80", required)
      dt
        label(for="animation") animation
      dd
        input#animation(type="checkbox", name="animation", checked)
      dt
        label(for="transparent") transparent
        small  /mix-blend-mode/
      dd
        select#transparent
          optgroup(label="disable")
            option(label="no", value="")
          optgroup(label="enable")
            each i in ['normal', 'multiply', 'screen', 'overlay', 'darken', 'lighten', 'color-dodge', 'color-burn', 'hard-light', 'soft-light', 'difference', 'exclusion', 'hue', 'saturation', 'color', 'luminosity']
              option(label=i, value=i, selected=( i === 'darken' ))

    hr

    .text-center
      input(type="reset")


  textarea#textarea(cols="50", rows="10")
  .text-right
    button.btn(type="button", data-clipboard-target="#textarea") copy

#apply

script#corner-tpl(type="text/template")
  a.github-corner(href="${url}", title="Fork me on GitHub")
    svg(width="${size}", height="${size}", viewbox="0 0 250 250")
      title Fork me on GitHub
      path(d="M0 0h250v250")
      path.octo-arm(d="M127.4 110c-14.6-9.2-9.4-19.5-9.4-19.5 3-7 1.5-11 1.5-11-1-6.2 3-2 3-2 4 4.7 2 11 2 11-2.2 10.4 5 14.8 9 16.2", fill="currentColor", style="transform-origin:130px 110px")
      path.octo-body(d="M113.2 114.3s3.6 1.6 4.7.6l15-13.7c3-2.4 6-3 8.2-2.7-8-11.2-14-25 3-41 4.7-4.4 10.6-6.4 16.2-6.4.6-1.6 3.6-7.3 11.8-10.7 0 0 4.5 2.7 6.8 16.5 4.3 2.7 8.3 6 12 9.8 3.3 3.5 6.7 8 8.6 12.3 14 3 16.8 8 16.8 8-3.4 8-9.4 11-11.4 11 0 5.8-2.3 11-7.5 15.5-16.4 16-30 9-40 .2 0 3-1 7-5.2 11l-13.3 11c-1 1 .5 5.3.8 5z", fill="currentColor")

    style.
      .github-corner svg {
        position: absolute;
        ${dirX}: 0;
        ${dirY}: 0;
        ${trans}
        ${mixBlendMode}
        color: ${color};
        fill: ${fill};
      }
      ${animation}

blockquote.info
  | inspired from <a href="http://tholman.com/github-corners/">GitHub Corners</a>, and <a href="https://github.com/tholman/github-corners/issues/5#issue-116228491">issue</a>
!

CSS 

              
                textarea {
  display: block;
  width: 100%;
  margin-top: 2rem;
}

dl {
  margin-left: 2rem;
  margin-bottom: 1.5rem;
}

dt {
  padding-top: .5rem;

  label {
    font-weight: 900;
  }
}

.text-center {text-align: center; }
.text-right {text-align: right; }

*,
*::before,
*::after {
  box-sizing: border-box;
}

body {
  position: relative;
  margin: 0;
  min-height: 100vh;
  padding-top: 1px;
  padding-bottom: 5rem;
  background-image: linear-gradient(rgba(#0cc,.5), #fff 10%);
  color: #333;
}

.box {
  max-width: 30rem;
  margin: 0 auto;
}

.intro {
  width: 80%;
  padding-bottom: 1rem;
  margin: .5em auto 1em;
  text-transform: capitalize;
  border-bottom: 1px dashed #999;
  text-align: center;

  small {
    display: block;
    text-transform: none;
  }
}

small {
  opacity: .6;
  font-style: italic;
}

.info {
  position: absolute;
  bottom: 0;
  right: 0;
  margin: 1em;
  font-size: .9em;
  font-style: italic;
  font-family: serif;
  text-align: right;
  color: #999;

  a {
    color: inherit;
  }
}
!

JS 

              
                /* globals Clipboard */

let corner = {
  tpl: document.getElementById('corner-tpl').textContent.trim(),
  textarea: document.getElementById('textarea'),
  target: document.getElementById('apply')
};

let animationStyle = `
  .github-corner:hover .octo-arm {
    animation: octocat-wave .56s;
  }
  @keyframes octocat-wave {
    0%, 100% {transform: rotate(0); }
    20%, 60% {transform: rotate(-20deg); }
    40%, 80% {transform: rotate(10deg); }
  }`;

corner.form = document.getElementById('corner-opts');

let update = function () {
  let color = corner.form.color.value;
  let fill = corner.form.fill.value;
  let transparent = corner.form.transparent.value;
  let _animationStyle = corner.form.animation.checked ? animationStyle : '';
  let size = corner.form.size.value;
  let url = corner.form.url.value;

  let [ay, ax] = [].filter.call(corner.form.opts_pos, i => i.checked)[0].value
    .split('').map(i => i === '+' ? 1 : -1);

  let trans = (ay === 1 && ax === 1) ? '' : `transform: scale(${ax},${ay});`;

  let dirX = ax > 0 ? 'right' : 'left';
  let dirY = ay > 0 ? 'top' : 'bottom';

  if (transparent !== '') {
    transparent = `mix-blend-mode:${transparent};`;
  }

  let _tpl =
    corner.tpl

      // replace
      .replace(/\${url}/, url)
      .replace(/\${size}/g, size)
      .replace(/\${fill}/, fill)
      .replace(/\${color}/, color)
      .replace(/\${trans}/, trans)
      .replace(/\${dirX}/, dirX)
      .replace(/\${dirY}/, dirY)
      .replace(/\${mixBlendMode}/, transparent)
      .replace(/\${animation}/, _animationStyle)

      // minify
      .replace(/\s*([:{}; ])\s*/g, '$1')
      .replace(/>\s+?</g, '><');

  corner.target.innerHTML = corner.textarea.value = _tpl;
};

// init
(function () {
  update();

  // bind events
  new Clipboard('.btn');
  corner.form.addEventListener('input', update);
  corner.form.addEventListener('change', update);
  corner.form.addEventListener('reset', function () {
    setTimeout(update, 0);
  });
})();
!
999px

Console