Create an arrow in Sass and place on element.

arrow.scss

// Add dropdown to multiselect elements
.k-multiselect {
    position: relative;

    &:after {
        content: " ";
        width: 0;
        height: 0;
        position: absolute;
        top: 45%;
        right: 12px;
        border: 6px solid transparent;
        border-top-color: #444;
    }
}