You can use layout grid/table with two columns, in 1st you can place your input widget or dropdown and in 2nd you can put your button. You’ll have to do some CSS styling to make it look nice.
Here's what we do: wrap the input and the button with a container, set the container class custom-input-with-trigger-container add the following to the custom styles:
div.custom-input-with-trigger-container {
position: relative;
&> div {
&> div > input {
margin-right: 50px; /* margin-right also makes the border around input behave nice */
}
}
&> button {
position: absolute;
right: 0;
top: 0;
}
}