Minifed Examples found in Bootstarp.min.js
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calc (Keep space before and after + )
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calc(1.5em + .5rem + 2px);
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calc(1.5em + .5rem + 2px);
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>
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.form-floating > .form-control
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.form-floating>.form-control
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+
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legend + *
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legend+*
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+
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.btn-check:focus + .btn-primary
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.btn-check:focus+.btn-primary
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Keep space
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.nav-tabs .nav-link.active
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.nav-tabs .nav-link.active
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Explanation
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https://stackoverflow.com/questions/18858298/in-css-is-a-b-different-than-a-b
Is ".a.b" different than ".a .b"?
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Then answer is "Yes!"

".a.b" is one or more elements with both classes.
".a .b" is one or more elements with class b with any parent element with class a
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