css & focus-within & pseudo class
demo
:focus-within
https://developer.mozilla.org/en-US/docs/Web/CSS/:focus-within
https://caniuse.com/#feat=css-focus-within
pseudo class
https://developer.mozilla.org/en-US/docs/Web/CSS/Pseudo-classes
https://css-tricks.com/almanac/selectors/f/focus-within/
https://alligator.io/css/focus-within-pseudo-class/
https://davidwalsh.name/css-focus-within
https://usefulangle.com/post/128/css-focus-within
https://dev.to/laurieontech/focus-vs-focus-within-3748
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