Add responsive grid gaps to the default theme - #16

Changed pages include:

• index.html - view
• blog/index.html - view
• demos/index.html - view
• blog/colors-in-css/index.html - view
• blog/css-animation-fill-modes/index.html - view
• blog/css-animation-properties-cheat-sheet/index.html - view
• blog/css-container-queries-examples/index.html - view
• blog/css-context-aware-selectors/index.html - view
• blog/css-element-centering/index.html - view
• blog/css-logical-properties/index.html - view

There are more changes not included in the list