Источник: How To Create a Scroll Back To Top Button
Сначала добавляем кнопку средствами HTML.
<button onclick="topFunction()" id="myBtn" title="Go to top">Top</button>
Далее добавляем CSS.
#myBtn {
display: none; /* Hidden by default */
position: fixed; /* Fixed/sticky position */
bottom: 20px; /* Place the button at the bottom of the page */
right: 30px; /* Place the button 30px from the right */
z-index: 99; /* Make sure it does not overlap */
border: none; /* Remove borders */
outline: none; /* Remove outline */
background-color: red; /* Set a background color */
color: white; /* Text color */
cursor: pointer; /* Add a mouse pointer on hover */
padding: 15px; /* Some padding */
border-radius: 10px; /* Rounded corners */
font-size: 18px; /* Increase font size */
}
#myBtn:hover {
background-color: #555; /* Add a dark-grey background on hover */
}
Заключительный шаг - добавляем JavaScript.
//Get the button:
mybutton = document.getElementById("myBtn");
// When the user scrolls down 20px from the top of the document, show the button
window.onscroll = function() {scrollFunction()};
function scrollFunction() {
if (document.body.scrollTop > 20 || document.documentElement.scrollTop > 20) {
mybutton.style.display = "block";
} else {
mybutton.style.display = "none";
}
}
// When the user clicks on the button, scroll to the top of the document
function topFunction() {
document.body.scrollTop = 0; // For Safari
document.documentElement.scrollTop = 0; // For Chrome, Firefox, IE and Opera
}
Аналогичный пример на jQuery.