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See this CodePen: http://codepen.io/anon/pen/KypbC.

HTML

<body> <nav> <ul> <li>One</li> <li>Two</li> <li>Three</li> </ul> </nav> </body>

CSS

body { font-family: "Helvetica Neue"; } nav { height: 50px; background-color: #EEE; /* border: 1px solid #DDD; */} nav ul li { display: inline; padding: 20px; line-height: 50px; } .nav-inverse { background-color: black; color: lightGray; }

I know it has something to do with the line-height property, but don't understand how it works.

Edit: I've read through the documentation of line-height, but don't understand it.

  • What is a "line box"?
  • What makes an inline element "replaced" vs. "not replaced"? ...
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    This isn't relative to the border. You are facing "collapsing margins" see this example with 0 margin set on the ul (remember browsers give a default margin to them) codepen.io/web-tiki/pen/yBtur Commented Oct 5, 2014 at 14:50
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    more about collapsing margins (scroll down to "Collapsing Margins Between Parent and Child Elements") sitepoint.com/web-foundations/collapsing-margins Commented Oct 5, 2014 at 14:55
  • Thanks, that's helpful! Commented Oct 5, 2014 at 14:57

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The "issue" you are facing is related to collapsing margins between parent and child element.

Parent and first/last child

If there is no border, padding, inline content, or clearance to separate the margin-top of a block with the margin-top of its first child block, or no border, padding, inline content, height, min-height, or max-height to separate the margin-bottom of a block with the margin-bottom of its last child, then those margins collapse. The collapsed margin ends up outside the parent.

source : MDN

The default styling of the <ul> element includes margin-top. It collapses with the parent container (nav) when you don't give a border to it.

This is why th ul element "moves" down when you set a border to it.

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you should use display:inline-block and always use box-sizing:border-box which gives border inside or it will be 100% width + border 2px (right + left) so it will go beyond 100% and scroller will appear

the issue was you gave line-height + padding so the height increased

Codepen

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Why? I'm not particularly interested in getting it to work. I'm interested in learning why things work the way they do.

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