Elementor users may disregard most of settings in this tab, cause default color and style of Elementor buttons are configured in Elementor site settings. You can find more information here https://elementor.com/help/site-settings/
Nevertheless, you can also apply The7’s button style, which is configured under Theme Options -> Button. Edit the button and click on the global icon for the text (fig. 1) and background (fig. 2) and then select The7 colors for the text and background.
These options can be configured in the “Buttons color” tab (fig. 3). You need to specify button idle and hover colors for background, text and border: