Add themes in-tree

themes/github.com/davegallant/hugo-theme-gruvbox/assets/css/critical/00-vendor.css

@@ -0,0 +1,28 @@
+/*
+  Critical CSS for above-the-fold content, delivered inline to increase first
+  paint performance
+*/
+
+/*! purgecss start ignore */
+
+/* Typefaces */
+@import "typeface-roboto-slab";
+@import "typeface-fira-code";
+
+/* Normalize */
+@import "normalize.css/normalize.css";
+
+/*! purgecss end ignore */
+
+/*! CC BY-SA 3.0 License | https://stackoverflow.com/a/36118384/1154965 */
+@keyframes blink {
+  50% {
+    opacity: 0;
+  }
+  100% {
+    opacity: 1;
+  }
+}
+
+/* Default license header for non-vendor CSS source code that follows */
+/*! MIT License | github.com/schnerring/hugo-theme-gruvbox */