Add open-props topic

[SrGeneroso]

Please confirm this pull request meets the following requirements:

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• I am not the sole author or employee of a company who created either the topic I am modifying/adding or the collection entry I am modifying/adding.

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• Curating a new topic or collection
• Something that does not neatly fit into the binary options above

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Editing an existing topic or collection

I'm suggesting these edits to an existing topic or collection:

• Image (and my file is *.png, square, dimensions 288x288, size <= 75 kB)
• Content (and my changes are in index.md)

Please replace this line with an explanation of why you think these changes should be made.

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Open Props is a very thoughtful and comprehensive design tool that manages to be easy to use, beautiful and fully compatible with any project that uses CSS. It was made by Adam Argyle, who is one of the best advocates for CSS (He is currently working on google for the CSS group for chrome). Please consider this entry as it is the best way I can find to show some love to the project and the awesome community around it.

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• My suggested edits are not about an existing topic or collection, or at least not a single one
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Please replace this line with an explanation of your proposed changes.

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[jmeridth]

Couple requests. Thank you.

[jmeridth]

@SrGeneroso I can appreciate the excitement but can I ask that we remove this paragraph and stick to the facts about the topic? Thank you.

[SrGeneroso]

Sure, is line 21 ok? Those are features of the library.

[jmeridth]

Yes

[SrGeneroso]

Do I need to mend the commit or would you do the changes? I'm fine either way. Let me know.

[jmeridth]

@SrGeneroso we need to remove the open-props alias, it is redundant.