fix(docs): fix doc sidebar not in mobile with fixed

fix #29

Author: luchunyu

docs/layouts/component.vue

@@ -15,7 +15,7 @@
             )
               | {{sub.title}}
               span.is-text-gray-6.has-margin-left-sm(v-if="sub.name") {{ sub.name }}
-      c-box-item.content(xs=12 sm=8 md=9 lg=10)
+      c-box-item.content(xs=12 sm="8 offset-4" md="9 offset-3" lg="10 offset-2")
         transition(name='fade')
           router-view.c-container.is-lg
         c-footer

docs/styles/theme.css

@@ -86,7 +86,6 @@
 }
 
 .main {
-  height: calc(100vh - 4em);
   margin-top: 4em;
 
   & .sidebar,
@@ -95,13 +94,19 @@
   }
 
   & .sidebar {
-    position: relative;
+    position: fixed;
+    height: calc(100vh - 4em);
     background: #fff;
     box-shadow: 0 0 6px rgba(0, 0, 0, 0.15);
     padding-bottom: 5em;
   }
 }
 
+[media="xs"] .main .sidebar {
+  position: relative;
+  height: auto;
+}
+
 .hero {
   width: 100%;
   min-height: calc(100vh - 9.04em);