harmonize colors of boxes with frozen

_sass/minima/_boxes.scss

-$COLOR_BOX_PRIMARY: #4085e4;
-$COLOR_BOX_SECONDARY: #808080;
-$COLOR_BOX_FONT: #444;
+$COLOR_BOX_SECONDARY: darkgrey;
+$COLOR_BOX_FONT: #666666;
 
 .index-box-container {
     columns: 2;