如何在wordpress图像/主页上添加颜色叠加层 - 或不透明度下降？ （前悬停）

How do I add an color overlay or maybe an opacity drop the the images on a wordpress homepage - they have a color overlay on hover - but I want them to be darker in the picture color, as I am trying to go with a dark theme.How do I add an color overlay or maybe an opaci