Forest theme

[jienagu]

Hi Yihui,

This PR includes a few features:

1. Since you are using darkslategray color, I change the header with a similar color and body with a lighter color. That is why this PR is called "forest".
   

2. I add a few hover effects on each block to make it more interactive.

3. For the postcard block, considering the summary text of just the header of the post, which might be meaningless (sometimes), I try to put a feature to allow use put a few words (real) summaries or an image of this post, which I assigned to postShort class. Then when the user hovers over the short-term summary, the header text pops up.
   

Welcome any feedback! Thank you!

[lucharo]

I know it's been 3 years but I really like the look of this, any chance of merging it?

[yihui]

You don't have to wait for the PR to be merged but can use the forest_theme branch. If you use blogdown to create a new site, the theme argument can take the value yihui/hugo-prose@forest_theme.