<div id="btn_(тут скрипт)">Кнопка</div>

var colors = ['pink', 'black', 'yellow', 'blue', 'red', 'orange', 'gray', 'white'];
var len = colors.length;
var n = (len - Math.random() * (len-1)).toFixed(0) - 1;
alert(colors[n]);

function u_fav(url){
      var l = document.getElementsByTagName('link');
      for(i = 0;i <= l.length - 1;i++){
   if(l[i].hasAttribute('type')){
       if(l[i].getAttribute('type') == 'image/x-icon'){
    l[i].parentNode.removeChild(l[i]);
       };   
   };
      };
   document.head.insertAdjacentHTML('AfterBegin','<link href="'+url+'" type="image/x-icon" rel="shortcut icon">');
  };

<a href="javascript://" onclick="u_fav('http://usite.su/favicon.ico');">Изменить фавикон</a>

function setCookie(name, value, days) {
   if (days) {
    var date = new Date();
    date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
    var expires = "; expires=" + date.toGMTString();
   }
   else var expires = "";
   document.cookie = name + "=" + value + expires + "; path=/";
}
     
function getCookie(name) {
   var nameEQ = name + "=";
   var ca = document.cookie.split(';');
   for (var i = 0; i < ca.length; i++) {
    var c = ca[i];
    while (c.charAt(0) == ' ') c = c.substring(1, c.length);
    if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length, c.length);
   }
   return null;
}
     
function eraseCookie(name) {
   setCookie(name, "", -1);
}

<div id="other_element">text and other..</div>

<button id="but_cookie"></button>

<script type="text/javascript">
if(getCookie('b_c') == 1){
b_c('f');
} else{
b_c('a');
};
function b_c(t){
if(t == 'f'){
setCookie('b_c',1,365);
document.getElementById('other_element').style.position = 'fixed';
document.getElementById('but_cookie').innerText = 'Поменять на absolute';
document.getElementById('but_cookie').setAttribute('onclick','b_c(\'a\');');
} else if(t == 'a'){
setCookie('b_c',0,365);
document.getElementById('other_element').style.position = 'absolute';
document.getElementById('but_cookie').innerText = 'Поменять на fixed';
document.getElementById('but_cookie').setAttribute('onclick','b_c(\'f\');');
};
};
</script>

Станислав, недавно с js начал работать?