To define the Menu icon and Expanded Panel, please go to ART Theme > Theme Options > Header.
You could set the menu icon style, size, and spacing.
You could define the icon size by the icon height option. Please enter the integer number. It will be shown by the default size if they are empty. The default for Desktop is 26, for Mobile is 16.
The expanded panel will be shown when menu icon is clicked.
There are the options for spacing of menu items and align.
There are 2 options for the sub-menu style, they are 2 kinds of interactive rule:
For the 1st sub-menu style:
Please note that the level-1 menu item which has the sub-menu cannot be linked a webpage(URL).
For the 2nd sub-menu style:
The interactive rule of the 2nd option is that when you click the level-1 menu (including the text and arrow on the right), you can open the sub-menu. After opening the sub-menu, click the text of the level-1menu to link to the URL of the level-1 menu item, click the arrow of the level-1 menu, you can close the sub-menu.
PS: please check how to create a sub-menu in WordPress
If you want to define the color(Background color and element color) for the Expanded panel, please go to Theme Options > Colors: Expanded Panel