plastik-horizontal-multiselect.css

:host {
    border: 1px solid #ddd;
    border-radius: 2px;
    text-align: center;
}

polyfill-next-selector {
    content: ':host, :host > core-item, :host > paper-item';
}

:host, ::content > core-item, ::content > paper-item {
    background-color: #fff;
    display: -ms-flexbox;
    display: -webkit-flex;
    display: flex;
    -ms-flex-direction: row;
    -webkit-flex-direction: row;
    flex-direction: row;
    max-width: none;
    width: auto;
    min-width: 50px;
    -webkit-user-select: none;
    -moz-user-select: -moz-none;
    user-select: none;
}

polyfill-next-selector {
    content: ':host > core-item, :host > paper-item';
}

::content > core-item, ::content > paper-item {
    cursor: pointer;
}

polyfill-next-selector {
    content: ':host > core-item';
}

::content > core-item {
    padding: 0 8px;
}

@media (max-width: 780px) {
    polyfill-next-selector {
        content: ':host';
    }

    :host {
        -ms-flex-wrap: wrap;
        flex-wrap: wrap;
    }

    polyfill-next-selector {
        content: ':host > core-item, :host > paper-item';
    }

    ::content > core-item, ::content > paper-item {
        flex-grow: 1;
        min-width: 33.333%;
    }
}

polyfill-next-selector {
    content: ':host > core-item, :host > paper-item';
}

::content > core-item, ::content > paper-item {
    -ms-flex-pack: center;
    -webkit-justify-content: center;
    justify-content: center;
    color: #212121; /* Approximation of rgba(0, 0, 0, .87) on white */
    color: rgba(0, 0, 0, .87);
    font-weight: 400;
}

polyfill-next-selector {
    content: ':host > core-item.core-selected, :host > paper-item.core-selected';
}

::content > core-item.core-selected, ::content > paper-item.core-selected {
    background-color: #009688; /* Material Design Palette Teal 500 */
    color: #fff;
    font-weight: 500;
}

core-item::shadow .button-content, paper-item::shadow .button-content {
    text-align: center;
}