jasaraharja/public/vendor/select2-bootstrap4-theme-ma.../src/_single.scss

.select2-container--bootstrap4 {
    .select2-selection--single {

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

        // placeholder
        .select2-selection__placeholder {
            // #757575 is same color of placeholder (on Chrome)
            color: #757575;
            line-height: $input-height-inner;
        }

        // arrow
        .select2-selection__arrow {
            position: absolute;
            top: 50%;
            right: 3px;
            width: 20px;

            b {
                top: 60%;
                border-color: $dark transparent transparent transparent;
                border-style: solid;
                border-width: 5px 4px 0 4px;
                width: 0;
                height: 0;
                left: 50%;
                margin-left: -4px;
                margin-top: -2px;
                position: absolute;
            }
        }

        // selected item
        .select2-selection__rendered {
            line-height: $input-height-inner;
        }
    }
}

// search box
.select2-search--dropdown .select2-search__field {
    border: $input-border-width solid $input-border-color;
    border-radius: $input-border-radius;
}

// no result message
.select2-results__message {
    color: $secondary;
}