How does sass or postcss style two adjacent elements?

for example:

<div class="demo">
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
</div>

now I want to set the font size of the two adjacent elements when the div mouse under demo rolls. How do I write this code?

Nov.30,2021

prev-sibling cannot be achieved by relying solely on css at this stage

next-sibling can still be done
.demo > div:hover + div {font-size: 2em;}

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MySQL Errno : 1021
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