Please use css like this to override default value

ng-multiselect-dropdown /deep/ .multiselect-dropdown > .dropdown-btn{
   font-size:12px !important;
}

Alternative

:host /deep/ .multiselect-dropdown .dropdown-btn {
   font-size:12px !important;
}

Please use css like this to override default value

ng-multiselect-dropdown /deep/ .multiselect-dropdown > .dropdown-btn{
   font-size:12px !important;
}

##Alternative

:host /deep/ .multiselect-dropdown .dropdown-btn {
   font-size:12px !important;
}

##Add to global style src/styles.css

.custom-font-size .multiselect-dropdown .dropdown-btn {
   font-size:12px !important;
}

then add this class custom-font-size to dropdown component

<ng-multiselect-dropdown class="custom-font-size"></ng-multiselect-dropdown>

Please use css like this to override default value

ng-multiselect-dropdown /deep/ .multiselect-dropdown > .dropdown-btn{
   font-size:12px;
}

Please use css like this to override default value

ng-multiselect-dropdown /deep/ .multiselect-dropdown > .dropdown-btn{
   font-size:12px !important;
}

Alternative

:host /deep/ .multiselect-dropdown .dropdown-btn {
   font-size:12px !important;
}