set the opacity only to background color not on the text in css code example
Example: background color opacity
rgba(51, 170, 51, .1) /* 10% opaque green */
rgba(51, 170, 51, .4) /* 40% opaque green */
rgba(51, 170, 51, .7) /* 70% opaque green */
rgba(51, 170, 51, 1) /* full opaque green */