STYLE: more yellow color for output blocks
STYLE: more yellow color for output blocks

To differentiate more with code blocks for themes where they are white.

Yellow is a neutral color, that is not used for code in any major theme.

Titan-C/sphinx-gallery,Eric89GXL/sphinx-gallery,sphinx-gallery/sphinx-gallery,sphinx-gallery/sphinx-gallery,Eric89GXL/sphinx-gallery,lesteve/sphinx-gallery,Titan-C/sphinx-gallery,lesteve/sphinx-gallery