To do that you have the opportunity to append the dropdown to any element you want with the drop-down-append-to attribute, which accepts a CSS selector.
Have a look at the following example: codepen.
In it, the dropdown is appended to the body, you can also change the position of the dropdown with the drop-down-position attribute.
Here is a link for ComboBox`s API: https://www.htmlelements.com/docs/combobox-api

You can also change these properties programmatically:

const combobox = document.querySelector('smart-combo-box');

combobox.dropDownAppendTo('body'); //the value should be CSS selector

combobox.dropDownPosition = 'bottom'; //possible values are:
//'auto', 'top', 'bottom', 'overlay-top', 'overlay-center', 'overlay-bottom', 'center-bottom', 'center-top'

If you have any additional questions, do not hesitate to ask!

Best Regards,
Svetoslav Borislavov

Smart UI Team