Selection highlight of code is inconsistent

[cchaos]

Some parts of the code coloring changes the color (or removes) the text highlight when the text is selected.

The issue stems from this selector:

eui/src/components/code/_code_block.scss

Lines 95 to 97 in cb33008

	.hljs > *::selection {
	background-color: $euiCodeBlockSelectedBackgroundColor;
	}

Which compiles to:

 .euiCodeBlock .hljs > *::selection {
    background-color: inherit;
}

Removing that selector fixes the highlighting. Or we need to give it an explicit value.