Please Help With Custom CSS

Hello!
I am trying to fit Ivory Search in the home of this “under construction” website: https://dizionariodeisogni.it/
I am using “Voice” plugin and I inserted shortcode that is showing in the “block” … anyway, Ivory Search Form occupies just a portion (a quarter?) of the box width, and the Search Button is on a “new line”

Using this CSS code:

.is-search-input {
	width: 600px !important
}

Search button stays under the form and not on its right. Now I removed the code from custom CSS .. could please help me with the right code I may use to get a form fitting the box?

Would It be also responsive with mobile devices?

Thanks!