Basic CSS embed style

Hi - does anyone know how can i style this search filter element

Screenshot 2020-09-16 at 15.24.56

to something that looks like this

Screenshot 2020-09-16 at 15.25.03

Basically I just need to replace the color white with transparent and put a white line at the bottom with 1px thickness. Perhaps if there is also a way to add a text that says “filter”…

This is the page: https://www.sharp-studio.com/dms

or at least if anyone know if there is a guide on how to style using code

Thank you.
G


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