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I recently ran into a situation where some of my styles were broken in Internet Explorer 8. What makes this different from all the other times my styles broke in IE8 was that, as far as I could tell, it was correct. Consider the following code: %highlighted { background-color: #ff0; color: #333; } .keyword.is-active { @extend %highlighted; padding: 10px; text-transform: uppercase; } No problem, right? Then why isn't it working? I wasn't sure, until I looked at the compiled CSS and saw something like this: .some-list:nth-child(2n), .is-highlighted, .keyword.is-active { background-color: #ff0; color: #333; } .keyword.is-active { padding: 10px; text-transform: uppercase; } Since IE8 doesn't support the css selector nth-child , it ignores the entire rule . Without looking at the final output, there's no way of knowing if this will happen ahead of time. So what can you do? Well,

In Chris Coyier's recent article, " Fun with line-height! ", he mentions that we often use unitless values for line-height so that it's proportional to the font size. This is only part of the story, and I was reminded of a Stack Overflow question that got me investigating more about how line-height worked with regards to the various CSS units. If you're declaring the line-height on each element, you won't notice any difference. But if you're not crazy and using the first C of CSS (that's 'Cascading', by the way), then the inherited line-height might not work the way you expect. Disclaimer: This is my understanding after doing some research and testing. I may not be completely correct. TL;DR When using a relative unit (em, %), the line-height is calculated based on the font size of the element where the line-height is defined. This line-height is then inherited, unchanged, by each of its descendants. So we end up with a line