Generate computed css styles for all browsers. Puts the output into a textarea on the page (so it can be easily copied).

generate-computed-styles.js

// Generate computed styles to compare differences between two
function generateComputedStyles(selector, pseudoEl) {
  // https://stackoverflow.com/a/26878397
  var styles = [], css, el = document.querySelector(selector);
  if (el) {
    var computedStyle = window.getComputedStyle(el, pseudoEl);
    for (var i = computedStyle.length; i--;) {
      var propertyName = computedStyle[i];
      var propertyValue = computedStyle.getPropertyValue(propertyName);
      if (!propertyValue) {
        continue; // Skip empty values
      }
      //propertyName = propertyName.replace(/(^(ms|webkit)|[A-Z])/g, function (x) { return '-' + (x.toLowerCase()) });
      styles.push(propertyName + ': ' + propertyValue);
    }
    var t = document.getElementById('css-styles');
    if (!t) {
      t = document.createElement('textarea');
      t.id = 'css-styles';
      t.setAttribute('readonly', '');
      document.body.appendChild(t);
    }
    css = t.value = styles.sort().join(';\n');
    // Attempt to copy the styles.
    //t.select(); document.execCommand('copy');
  }
  return css;
}
//generateComputedStyles('#element-selector', ':before');