fix documentation CSS

- make documentation usable on small (narrow) screens
- slightly smaller font size in tables
- fix search input width

config/nimdoc.cfg

@@ -231,25 +231,35 @@ body {
 .columns {
   width: 100%;
   float: left;
-  box-sizing: border-box; }
+  box-sizing: border-box;
+  margin-left: 1%;
+}
 
-  .column,
-  .columns {
-    margin-left: 1%; }
+.column:first-child,
+.columns:first-child {
+  margin-left: 0; }
 
-  .column:first-child,
-  .columns:first-child {
-    margin-left: 0; }
+.three.columns {
+  width: 19%; }
 
+.nine.columns {
+  width: 80.0%; }
+
+.twelve.columns {
+  width: 100%;
+  margin-left: 0; }
+
+@media screen and (max-width: 860px) {
   .three.columns {
-    width: 19%; }
-
+    display: none;
+  }
   .nine.columns {
-    width: 80.0%; }
-
-  .twelve.columns {
-    width: 100%;
-    margin-left: 0; }
+    width: 98.0%;
+  }
+  body {
+    font-size: 1em;
+    line-height: 1.35;
+  }
 }
 
 cite {
@@ -261,7 +271,7 @@ div#searchInputDiv {
   margin-bottom: 1em;
 }
 input#searchInput {
-  width: 145px;
+  width: 80%;
 }
 
 
@@ -608,7 +618,9 @@ table {
   margin-bottom: 1.5em;
   border-collapse: collapse;
   border-color: #ccc;
-  border-spacing: 0; }
+  border-spacing: 0;
+  font-size: 0.9em;
+}
 
 table th, table td {
   padding: 0px 0.5em 0px;