How can a URL fragment affect a CSS layout?

Question

Compare these 3 URLs (look at the top navigation bar in each case):

1. http://fast.kirkdesigns.co.uk/blog
2. as above but with the url fragment #navigation
3. as above but with the url fragment #node-2655

Note, that the only difference is the URL fragment on the end.

The first two pages display absolutely fine (in Firefox at least). It's the third one where the problem lies. The fragment #node-2655 pushes the top navbar off the top of the screen. When you then scroll back up to the top of the page, the navbar has been cut in half. This happens when using any URL fragment that causes the navbar to be out of the initial viewport when the page is first loaded.

So, how can using a url fragment affect the css layout like this?!

THE SOLUTION: as suggested below, removing the overflow: hidden on the container element that held the navbar fixed the problem. I'd love to understand why though!

Answer 1

Remove the overflow:hidden on #main in css_75afd7072eaf4096aaebf60674218e31.css

Answer 2

I'd say it's a rendering bug in FireFox as it's fine in Opera. There shouldn't be anyway an anchor would change the CSS like you say (unless you are using jQuery or something).

Answer 3

I am having this problem too, and think I can see what is happening.

The "column" block with the massive (5678 pixel) margin and padding makes that block very tall. In browsers other than Firefox, the positive and negative values cancel each other out, but FF really does make it that tall - kind of.

FF also knows the two cancel each other out, but seems to look at the 5678px padding and decides the column block is poking out the bottom of the #wrapper block. This is overflow - and with overflow set to auto on #wrapper, you see the true size of #wrapper with a scroll-bar down the side.

With overflow set to hidden, FF takes away the scrollbar, but still seems to scroll the contents of #wrapper so that the item the fragment points to is at the top of the page. This is normal behaviour for fragment links in scrollable blocks, but since there is no scrollbar, you cannot scroll the content back down again, hence it looks like the layout has been effected by the fragment.

So in short, I suspect that FF is operating an invisible scrollbar in this example. That could be considered a bug, but it is probably correct behaviour. Being able to scroll the content up and down inside a non-overflowed fixed-sized block using URL fragments, is a technique that can be used effectively to implement image "sliders" that work even in the absence of JavaScript.

Hope that helps. This has been puzzling me for years, and this explanation suddenly struck me out the blue. My current workaround for this is to use jQuery "scroll to" plugin to scroll the whole page down to the fragment, as this seems to prevent the contents of #wrapper from scrolling internally.

You can also take "display: hidden" off #wrapper, but your page then ends up half a mile long.

Answer 4

I'll just point out that there may be some weird inheritance from the 30+ stylesheets linked to in the head. There may not, either, and it's probably a rendering bug (possibly related to :target styling) that Dan suggested. I just felt it worth pointing out that if you've got more than thirty stylesheets, you likely to start seeing some weirdness, whatever else might happens.

Answer 5

The reason is the column with the large padding has expanded it's container, but the expansion is then hidden but overflow:hidden; but with the use of the fragment it is being scrolled into the position of the fragment, effectively chopping off anything above that. You can use javascript and set scrollTop to 0 and it scroll it back to the normal position.

Basically a wierd edge case which browsers do not seem to handle very well.

Answer 6

Sorry this isn't an "answer," tho it is a response to the other comments here. This problem is just flabbergasting. It is very easy to isolate (i.e., has nothing to do with number of stylesheets), and doesn't have a proper "solution," as there is no way to achieve the desired rendering.

<!DOCTYPE html>
<html>
<head>
<style>
#container {
  margin: 1em auto;
  width: 40em;
}
#wrapper {
  overflow: hidden;
  position: relative;
}
#c1 {background-color: #aaf;}
#c2 {background-color: #ccf;}
.column {
  float: left;
  margin-bottom: -5678px;
  padding-bottom: 5678px;
  width: 50%;
}
#footer {
  background-color: #eee;
  padding: 1px;
  text-align: center;
}
p {margin: 1em;}
</style>
</head>
<body>
<div id="container">
<div id="wrapper">
<div id="c1" class="column">
<p>This is some content in a short column. We would need some Javascript to change its height if we wanted a different background color for each column to stretch the full height of the respective columns...or we can use large padding together with an equal negative margin.</p>
<ul>
<li><a href="#p1">Jump to P1</a></li>
<li><a href="#p2">Jump to P2</a></li>
<li><a href="#p3">Jump to P3</a></li>
</ul>
</div>
<div id="c2" class="column">
<p id="p1">The desired effect is to have the height of the two columns appear the same. We use 'overflow:hidden' on the containing div (#wrapper) to wrap it around the floated columns.</p>
<p id="p2">These paragraphs have fragment identifiers. Problem comes in when clicking one of the links on the left. Instead of scrolling just the page, the browser scrolls the div with 'overflow:hidden' so the target is at the top. It does this even if the target is already visible.</p>
<p id="p3">Opera does not exhibit this behavior. This occurs in Chrome/Safari, Firefox, and IE. (Interestingly, IE also works as expected if we completely remove the DOCTYPE declaration.)</p>
</div>
</div>
<div id="footer">
<p>Footer stuff.</p>
<p>To see why 'overflow: hidden' (or any other piece of the CSS) is needed, just try disabling it.</p>
</div>
</div>
</body>
</html>

Answer 7

Just as a side-note, the above technique is generally used to provide flexible-width mulit-column layouts. This is probably becoming less important these days as fixed-width layouts are becoming a lot more comment - browsers are able to magnify the web page to see small text, and fixed-width makes it a lot easier to control the typography of a page, e.g. set the width (in ems) to display the ideal nine words per line regardless of what font size and magnification the user chooses.

Sorry if that does not sound like an answer, but it is basically suggesting to discard this old model and consider moving to fixed-width columns (which is a whole new subject).

Answer 8

I was able to solve this with some javascript to scroll the body to the position the overflow hidden element was scrolled to.

setTimeout(() => {
    let intendedScroll = document.getElementById("fragmentfix").scrollTop;
    document.getElementById("fragmentfix").scrollTop = 0;
    window.scrollTo(0, intendedScroll);
}, 0)