how to set background color opacity in css code example

Example 1: how to blur background color in css

background: rgba(255,255,255,0.5);
backdrop-filter: blur(5px);

Example 2: background color semi transparent

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

Example 3: css opacity background color

background: rgba(255, 255, 255, 0.25);

Example 4: css opacity example

.opacity30 {
  opacity: 0.3;
  filter: alpha(opacity=30); /* For IE8 and earlier */
}

Example 5: background color with opacity

h1 {background-color:rgba(255,0,0,0.3);}

Example 6: 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 */