Remove redundant properties from .embed-responsive

[MartijnCuppens]

We copied the .embed-responsive code from somewhere else, but there are a lot of redundant properties in it:

• No need to set display: block; on a <div>
• No need to remove padding from a <div>
• No need to set overflow: hidden; because the inner content is spread in .embed-responsive
• No need for bottom: 0;, because we already have height: 100%;

[ysds]

I want to hear @necolas 's thoughts.
29e495f#diff-57ae112f09250f95da6f28dfff1d519f

[MartijnCuppens]

I also wonder if this css:

.embed-responsive .embed-responsive-item,
.embed-responsive iframe,
.embed-responsive embed,
.embed-responsive object {
  ...
}

should be rewritten as:

.embed-responsive > * {
  ...
}

I know we better avoid the universal selector but I think for this case with the child combinator and the decrement of the number of selectors, it might be acceptable.

[mdo]

The biggest problems we had with selector performance issue we ever had was using them too much with attribute selectors for column classes. In these instances, I think it's acceptable. However, I'm curious if folks have other content within these elements? Does anything else accompany an embed other than the source?

[XhmikosR]

I believe it's better to err on the safe side and be as explicit as possible IMO.

[ysds]

I confirmed the CSS are correct in theory, and tested in IE11, Edge, Firefox and Chrome. Let’s merge this.

@MartijnCuppens Would you fix the conflict?

[MartijnCuppens]

Done

[MartijnCuppens]

This is a minor optimization, not worth backporting this to v4, it might break some edge cases.