How to optimize css with pseudo elements and transparency

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Optimize with pseudo elements and transparency

Optimized with pseudo elements and transparency, we add a before pseudo element to the above element, which is the same size as the parent div, and add the required final box shadow state to the element in advance, but the transparency of the element is 0.

Div {position: relative; width: 100px; height: 100px; box-shadow: 0 2px 4px rgba (0,0,0,0.3);} div::before {content: "; position: absolute; top: 0; left: 0; width: 100%; height: 100%; box-shadow: 0 5px 15px rgba (0,0,0,0.3); opacity: 0;}

Then, in hover, we just need to set the transparency of the pseudo element from 0 to 1.

Div:hover::before {opacity: 1;}

The advantage of this is that the actual shadow change is only a change in transparency, instead of constantly redrawing the shadow, which effectively improves the fluency of the shadow animation and makes it look more silky.

Why is it better to animate transparency opacity than to animate box-shadow? You can take a look at this table and list the effects of different attribute transformations on page rearrangement and redrawing:

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