How to write a selector with two non-nested classes?

as css or sass to write a selector that will apply to the unit which has both classes necessary? Through the gap you do not write well, because there is no nesting. Everything is generated dynamically and I don't know how many additional blocks will be, know that there is only 2 class on which to define a block, i.e. div+div is not going to work. Maybe missing something and the answer is obvious. Thank you for your help)
<div class="first"></div>
<div class="first second"></div>
<div class="second"></div>
April 3rd 20 at 18:37
1 answer
April 3rd 20 at 18:39
thank you) - robyn.Hansen30 commented on April 3rd 20 at 18:42

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