Update test-site: element "slider"

[annav00]

Update test-site: element "slider"

• [ ] background-color(name of material color or css color)
• [ ] theme (dark)
• [ ] dense (y/n)
• [ ] error-count (0-n)
• [ ] height (0-n)
• [ ] hide-details (y/n)
• [ ] hide-spin-buttons (y/n)
• [ ] loader-height (0-n)
• [ ] loading (y/n/color)
• [ ] success (y/n) ?
• [ ] success-messages (string) ?
• [ ] validate-on-blur (y/n)