How to make one side of the translucent?

Can't figure out how to make the left side otenok full-bodied, with the right side fully transparent fully. How did Vkontakte specify the mouse on the back button. Tried but nothing comes up
3da1672f4ba54e66becac1268bd22234.png
August 19th 19 at 22:49
2 answers
August 19th 19 at 22:51
it goes? https://jsfiddle.net/oyn0zv66/

You have in the screenshot, some decision. What is the question?
August 19th 19 at 22:53
Can multiple shadows in a row add to the same block, separated by commas. I hope more he will understand how and what to do.
box-shadow: #000 0 4px 6px, #000 0 4px 6px, #000 0 6px 4px;

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