Adding a main menu

The main menu UI resides under the Menu UI panel (under UI Canvas) in the scene hierarchy. We will add a menu panel with three buttons to let you add a cube, a sphere, and a virus. We'll create a menu sub-panel and arrange the menu buttons horizontally. Follow these steps:

1. In the Hierarchy, unfold the UI Canvas, and unfold its child Main UI object.
2. First, remove the temporary Main mode text element. Right-click the child Text object and select Delete.
3. Right-click the Menu UI and select UI | Panel, then rename it Main Menu.
4. On the Main Menu panel, use the Anchor Presets to set Bottom-Stretch, and use Shift + Alt + click Bottom-Stretch to make a bottom panel. Then set Rect Transform | Height to 175.
5. I set my background Image | Color to opaque white with Alpha: 255.
6. Select Add Component, search layout, then select | Horizontal Layout Group.
7. On the Horizontal Layout Group component check the Control Child Size | Width and Height checkboxes...