Beautify codes of playable area

[sutara79]

• Unify indent.
• Remove unnecessary space.
• Not to display unnecessary scroll bar.

Example:

/* Before */
.wrapper {
  display: flex;
}

.wrapper input[type="text"] {
    flex: 1 1 auto;
  }


/* After*/
.wrapper {
  display: flex;
}

.wrapper input[type="text"] {
  flex: 1 1 auto;
}

I am localizing Typical use cases of Flexbox.
Live example's codes are hard to read.
So I beautified it.
Please merge.

[sutara79]

I localized Backwards Compatibility of Flexbox in addition to above.
Then I noticed example's codes are hard to read.
Please consider to merge. (77e8883)

[avivmu]

@chrisdavidmills I suggest splitting this into two separate commits (I can do it if you will want) - formatting changes and visual changes.
The formatting could be trivially merged and the visual should be inspected to see if they add to the readability.