Image Post Grid Hover Background Color

I’ve looked through the code and edited what I thought was the right background color with no success. How do I change the background color when hovering over an image on the image post grid homepage? I have successfully reduced the opacity, but changing any background colors associated with that entity doesn’t do anything. I’d like the new background color to be #1a1a1a.

.image-post .text-holder:hover {
    opacity: 0.75;
	cursor: pointer;
	    background-color: #beb27a;    
		-webkit-transition: opacity .3s ease-in-out;
    -moz-transition: opacity .3s ease-in-out;
    -o-transition: opacity .3s ease-in-out;
    transition: opacity .3s ease-in-out;
}