Header appearing dark

Hi, I have uploaded a header image to wordpress using the big title section. The overlay appears too dark, much darker than the image is when uploaded. I have found a forum advising to type the following code into CSS:
.masthead-banner.data-bg:before {
background: rgba(0,0,0,0);
}
This hasn’t worked, so I am wondering if there is another issue?

Many thanks

Jane.

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