How can I increase the width of ng-dropdown-multiselect created using bootstrap AngularJs

You will have to override the CSS which is used to make the button with drop down.

Put the below CSS either inside the <script></script> or in some external CSS file which gets loaded before your html file.

.multiselect-parent .dropdown-toggle {
  width: 400px;
}

.multiselect-parent .dropdown-menu {
  width: 300px;
}

This would solve your issue.

Cheers!!!

This CSS works for me:

.multiselect-parent {
  width: 100%;
}

.multiselect-parent .dropdown-toggle {
  width: 100%;
}

.multiselect-parent .dropdown-menu {
  width: 100%;
}