我想在页面中居中"topofpage"。我在 CSS 中添加了"文本对齐：中心"，但是当它第一次开始滚动时它会跳跃/抽搐，将其稍微向右移动。如果没有添加的 CSS，它显示为左侧，并且在滚动时不会跳跃或猛拉。如何在滚动时没有跳跃/抖动的情况下居中页面顶部？
<div class="topofpage" id="mytopofpage">
<h2>My topofpage</h2>
</div>
/* Style the topofpage */
.topofpage {
padding: 10px 16px;
background: #555;
color: #f1f1f1;
text-align: center;
}
/* Page content */
.content {
padding: 16px;
}
/* The sticky class is added to the topofpage with JS when it reaches its scroll position */
.sticky {
position: fixed;
top: 0;
width: 100%
}
/* Add some top padding to the page content to prevent sudden quick movement (as the topofpage gets a new position at the top of the page (position:fixed and top:0) */
.sticky + .content {
padding-top: 102px;
}
// When the user scrolls the page, execute myFunction
window.onscroll = function() {myFunction()};
// Get the topofpage
var topofpage = document.getElementById("mytopofpage");
// Get the offset position of the navbar
var sticky = topofpage.offsetTop;
// Add the sticky class to the topofpage when you reach its scroll position. Remove "sticky" when you leave the scroll position
function myFunction() {
if (window.pageYOffset > sticky) {
topofpage.classList.add("sticky");
} else {
topofpage.classList.remove("sticky");
}
}
您必须将text-align: center;提供给.header或.topofpage类而不是sticky类，并将header类的填充更改为padding: 10px 0px;
.topofpage {
padding: 10px 0px;
background: #555;
color: #f1f1f1;
text-align: center;
}
window.onscroll = function() {myFunction()};
var header = document.getElementById("myHeader");
var sticky = header.offsetTop;
function myFunction() {
if (window.pageYOffset > sticky) {
header.classList.add("sticky");
} else {
header.classList.remove("sticky");
}
}body {
margin: 0;
font-family: Arial, Helvetica, sans-serif;
}
.top-container {
background-color: #f1f1f1;
padding: 30px;
text-align: center;
}
.header {
padding: 10px 0px;
background: #555;
color: #f1f1f1;
text-align: center;
}
.content {
padding: 16px;
}
.sticky {
position: fixed;
top: 0;
width: 100%;
}
.sticky + .content {
padding-top: 102px;
}<div class="top-container">
<h1>Scroll Down</h1>
<p>Scroll down to see the sticky effect.</p>
</div>
<div class="header" id="myHeader">
<h2>My Header</h2>
</div>
<div class="content">
<h3>On Scroll Sticky Header</h3>
<p>The header will stick to the top when you reach its scroll position.</p>
<p>Scroll back up to remove the sticky effect.</p>
<p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p>
<p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p>
<p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p>
<p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p><p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p> <p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p><p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p> <p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p><p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p> <p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p><p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p>
<p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p>
<p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p>
<p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p>
<p>Some text to enable scrolling.. Lorem ipsum dolor sit amet, illum definitiones no quo, maluisset concludaturque et eum, altera fabulas ut quo. Atqui causae gloriatur ius te, id agam omnis evertitur eum. Affert laboramus repudiandae nec et. Inciderint efficiantur his ad. Eum no molestiae voluptatibus.</p>
</div>这与box-sizingcss属性有关。默认情况下，它设置为content-box这会导致大小问题，因为边框/填充被添加到宽度的顶部。
你可以添加这个css来修复它：
* {
box-sizing: border-box;
}
请参阅：https://developer.mozilla.org/en-US/docs/Web/CSS/box-sizing