It takes as much energy to wish as it does to plan. — Eleanor Roosevelt
After just playing with apsect-ratio and being pleasantly surprised at how intuitive it is, here’s an example of CSS acting unintuitively:
… Read article “On fixed elements and backgrounds”If you have a fixed element on your page, which means it doesn’t move when you scroll, you might realise that it no longer acts fixed if you apply a CSS filter on its nearest ancestor. Go ahead, try it on the CodePen.
This is because applying a
filteron the fixed element’s immediate parent makes it
position: relative creates a new context for absolute positioning within an element? Well, position: sticky is a locally scoped version of position: fixed. Let's take a look at how that works using a modal with a sticky close button as an example. 
File this into a category of personal “CSS Ah-Ha Moments“.
The background-attachment property has never seemed all that useful to me. I have always looked at it as some sort of old school design trick from the GeoCities days to get a repeating background to stay in place during scroll.… Read article “Use Cases for Fixed Backgrounds in CSS”