how to set only background color opacity in css code example

Example 1: 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 */

Example 2: background having opacity and text above to not have opacity

background-color: rgba(255,0,0,0.6);