Demos: Update details to remove inline styles

Picked from @cfarquharson update in gh-1233
Colours: Fix padding for nested Summary background and tables

From @  cfarquharson's gh-1233 to address Detail Example 3
Merge pull request #1279 from nschonni/update-details-docs-split1233

Demos: Update details to remove inline styles
Set min-widths for 100% wide containers to resolve #1530.
Increased specificity of placeholder names.
Merge pull request #1780 from pjackson28/v3.0

Set min-widths for 100% wide containers to resolve #1530
Fixed issues raised in pull request #1780.
Merge pull request #1781 from pjackson28/v3.0

Fixed issues raised in pull request #1780
Resolved merge conflicts.