Custom css

Source

index.html

<!-- Custom style -->
<style>
cn-multiselect{
      --cn-multiselect-background-color-selected-option: #2e8555;
      --cn-multiselect-border-color-selected-option: #2e8555;
      --cn-multiselect-border-radius: 5px;
      --cn-multiselect-background-color-selected-checkbox: #2e8555;
      --cn-multiselect-border-color-selected-checkbox: #2e8555;
      --cn-multiselect-border-color: #2e855554;
      --cn-multiselect-border-color-checkbox: #2e855554;
      --cn-multiselect-bulk-actions-button-background-hover: #2e8555;
      --cn-multiselect-font: Verdana;
      --cn-multiselect-font-size: 22px;
}
</style>

<cn-multiselect
    title="Select country"
    selected='["IT"]'
    search="true"
    select-all="true"
    options='[{"value":"IT", "label":"Italy","style":{"backgroundColor":"#5ba9f5","borderColor":"#5ba9f5"}},{"value":"FR", "label":"France"},{"value":"ES", "label":"Spain"}]'>
</cn-multiselect>

Output