[Vuejs]-How can I set opacity in dropdown while selecting options?

You can make the background with opacity like this:

.multiselect__option--highlight {
    background: rgba(65, 184, 132, .3);
    outline: none;
    color: #fff;
}

and if you want the words "Please enter to select" also with opacity you can do it like this:

.multiselect__option--highlight {
    background: #41b883;
    outline: none;
    color: #fff;
    opacity: .3;
}