You can change the appearance of the search bar to match your phone's theme through the Google Help Center : Open the on your phone.
: Switch between standard, dark mode, or a custom color. Transparency : Make the bar more or less see-through. Shape : Change the bar from a rectangle to rounded edges. Managing the Widget Google Search Bar Widget
Select the widget, then tap and hold it to drag it onto your home screen. iOS Devices (iPhone/iPad) : You can change the appearance of the search