how to make slightly transparent background in css code example

Example 1: background color semi transparent

.transparent {
    background-color: rgba(255, 255, 255, 0.5);
}
.transparent {
    opacity: 0.5;
}

Example 2: css how to make background transparent

/* Use RGBA */
background-color: rgba(255, 255, 0, 0.75); /* Transparent Yellow */

Example 3: 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 */