If locked - set a specified background color to the row/card

[ildar170975]

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When the row/card is locked, the whole row/card has a specified background-color:

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The background may be set as a CSS style to the div#overlay element:

    background: rgba(66, 66, 66, 0.1);

The color must be specified by an option: background_locked: rgba(...) or not specified (default)

Also, a special CSS variable may be defined to set the background color for cards in HA.

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