Search Input Box
You can find the settings in section:
UI Settings -> Search Input Box -> Template for Search Input Box Defines the layout and color theme for the Search Input. Select one of these to render the Search Input box.
Text for Empty Search Box This text appears in the text box before the user starts typing inside the text box. A common example is Input your search…. When you focus on the input box you will see this text. All the out-of-the-box templates support this setting, but some template developers can choose to ignore this. Also, note that this setting supports localization in languages defined for the portal.
Name of Query String Parameter This setting allows you to adjust the name of the Query String parameter that passes the search term between the input box and the search results module. This makes it possible to integrate the search box with other search results module with GET, which allows you to customize the name of the Query String parameter. Read the article, Integrating the Search Boost Input module with Standard DNN Results module for more information.
Filters -> Portal Filter This allows the user to narrow searches to a specific portal.
Search Boost comes with 6 input templates: default, default-white, expandable, material-design, material-design-purple and orange-wide.