Z-index utilities

Use the following classes to quickly set a z-index:

• ecl-u-z-auto: Default z-index (auto)
• ecl-u-z-zero: No z-index (0)
• ecl-u-z-highlight: Used for more important elements (1)
• ecl-u-z-navigation: Used for navigation elements (10)
• ecl-u-z-dropdown: Used for dropdown elements (15)
• ecl-u-z-modal: Used for modal elements (20)
• ecl-u-z-max: Very high z-index (9999)