how to set background transparent in css code example

Example 1: css how to make background transparent

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

Example 2: css transparent background color

div {
 opacity:25% ; 
}

Example 3: change transparancy img css

img {
  opacity: 0.5;
}

Example 4: reduce opacity of background image css

.img1 {
opacity: 0.6;
z-index=1;
}