Use rem for gutters

Those are more stable for nested grids

Author: James Kolce

_globals.scss

@@ -104,7 +104,7 @@ $full-grid: false !default;
 $container-width: 1200px !default;
 
 // Gutter size
-$gutter: 2em !default;
+$gutter: 2rem !default;
 
 // Number of columns in a row
 $num-columns: 12 !default;

dist/concise.css

@@ -626,15 +626,15 @@ table {
   margin-left: auto;
   margin-right: auto;
   max-width: 1200px;
-  padding-left: 1em;
-  padding-right: 1em; }
+  padding-left: 1rem;
+  padding-right: 1rem; }
 
 [grid] {
   display: -webkit-box;
   display: -ms-flexbox;
   display: flex;
-  margin-left: -1em;
-  margin-right: -1em;
+  margin-left: -1rem;
+  margin-right: -1rem;
   -webkit-box-orient: vertical;
   -webkit-box-direction: normal;
       -ms-flex-direction: column;
@@ -650,8 +650,8 @@ table {
   -webkit-box-flex: 1;
       -ms-flex: 1;
           flex: 1;
-  padding-left: 1em;
-  padding-right: 1em; }
+  padding-left: 1rem;
+  padding-right: 1rem; }
 
 [grid~="ng"] {
   margin-left: 0;