_multiple.scss

.select2-container--bootstrap4 {
    .select2-selection--multiple {

        // height of input box
        min-height: $input-height !important;

        // input box
        .select2-selection__rendered {
            box-sizing: border-box;
            list-style: none;
            margin: 0;
            padding: 0 5px;
            width: 100%;
        }

        // each selected item in input box
        .select2-selection__choice {
            color: $dark;
            border: 1px solid darken($light, 20%);
            border-radius: $btn-border-radius-sm;
            padding: 0;
            padding-right: 5px;
            cursor: pointer;
            float: left;
            margin-top: 0.3em;
            margin-right: 5px;
        }

        // x button of each selected item in input box
        .select2-selection__choice__remove {
            color: darken($light, 20%);
            font-weight: bold;
            margin-left: 3px;
            margin-right: 1px;
            padding-right: 3px;
            padding-left: 3px;
            float: left;

            &:hover {
                color: $dark;
            }
        }
    }
}