added sticky footer

Author: yimingzhaomath

_sass/_base.scss

@@ -1,6 +1,11 @@
 /* ==========================================================================
    BASE ELEMENTS
    ========================================================================== */
+html {
+  /* sticky footer fix */
+  position: relative;
+  min-height: 100%;
+}
 
 body {
   margin: 0;
@@ -306,4 +311,4 @@ nav {
 b, i, strong, em, blockquote, p, q, span, figure, img, h1, h2, header, input, a, tr, td, form button, input[type="submit"], .btn, .highlight, .archive__item-teaser {
   -webkit-transition: $global-transition;
   transition: $global-transition;
-}
+}