How to put black overlay with opacity on a group of photos

Pass: bconsult

How do I put a black color overlay over the images and change the opacity? 

Also, is there a better way to write this code out? All 6 are for the same thing but different block ID's 

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www.elevatesportsventures.com/b-consult-copy

pass: bconsult

I added the link to the initial post

#block-22ab3ad3783e13aaba24,
#block-4783b3e592a2eb41c865,
#block-61f3b30b9a5d193a8bf4,
#block-cfc169501362045abc19,
#block-d88d1e086ec1a60012c8,
#block-df95fc0e382a9307298c

  {
  
    border : 1px solid #fff;
    
    }