Invert Page Booksmarklet

as said!

HTML

<button id='but_1' onclick="javascript: (
function () { 
    var css = 'html {-webkit-filter: invert(100%);' +
        '-moz-filter: invert(100%);' + 
        '-o-filter: invert(100%);' + 
        '-ms-filter: invert(100%); }',
    head = document.getElementsByTagName('head')[0],
    style = document.createElement('style');

if (!window.counter) { window.counter = 1;} else  { window.counter ++;
if (window.counter % 2 == 0) { var css ='html {-webkit-filter: invert(0%); -moz-filter: invert(0%); -o-filter: invert(0%); -ms-filter: invert(0%); }'}
 };

style.type = 'text/css';
if (style.styleSheet){
  style.styleSheet.cssText = css;
} else {
  style.appendChild(document.createTextNode(css));
}

head.appendChild(style);
 }());
">Invert</button>

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