feat($theme-default): using '.theme-default-content' to replace '.content' in <Content /> outlet.

packages/@vuepress/theme-default/components/Home.vue

@@ -38,7 +38,7 @@
       </div>
     </div>
 
-    <Content class="content custom"/>
+    <Content class="theme-default-content custom"/>
 
     <div
       class="footer"

packages/@vuepress/theme-default/components/Page.vue

@@ -2,7 +2,7 @@
   <main class="page">
     <slot name="top"/>
 
-    <Content class="content"/>
+    <Content class="theme-default-content"/>
 
     <footer class="page-edit">
       <div

packages/@vuepress/theme-default/styles/index.styl

@@ -4,6 +4,8 @@
 @require './wrapper'
 @require './toc'
 
+$contentClass = '.theme-default-content'
+
 html, body
   padding 0
   margin 0
@@ -53,22 +55,26 @@ body
   border-right 1px solid $borderColor
   overflow-y auto
 
-.content:not(.custom)
+{$contentClass}:not(.custom)
   @extend $wrapper
   > *:first-child
     margin-top $navbarHeight
+
   a:hover
     text-decoration underline
+
   p.demo
     padding 1rem 1.5rem
     border 1px solid #ddd
     border-radius 4px
+
   img
     max-width 100%
 
-.content.custom
+{$contentClass}.custom
   padding 0
   margin 0
+
   img
     max-width 100%
 
@@ -94,6 +100,7 @@ blockquote
   border-left .5rem solid #dfe2e5
   margin 0.5rem 0
   padding .25rem 0 .25rem 1rem
+
   & > p
     margin 0
 
@@ -106,15 +113,19 @@ strong
 h1, h2, h3, h4, h5, h6
   font-weight 600
   line-height 1.25
-  .content:not(.custom) > &
+
+  {$contentClass}:not(.custom) > &
     margin-top (0.5rem - $navbarHeight)
     padding-top ($navbarHeight + 1rem)
     margin-bottom 0
+
     &:first-child
       margin-top -1.5rem
       margin-bottom 1rem
+
       + p, + pre, + .custom-block
         margin-top 2rem
+
   &:hover .header-anchor
     opacity: 1
 
@@ -136,6 +147,7 @@ a.header-anchor
   padding-right 0.23em
   margin-top 0.125em
   opacity 0
+
   &:hover
     text-decoration none
 
@@ -157,6 +169,7 @@ table
 
 tr
   border-top 1px solid #dfe2e5
+
   &:nth-child(2n)
     background-color #f6f8fa
 
@@ -168,10 +181,12 @@ th, td
   &.sidebar-open
     .sidebar-mask
       display: block
+
   &.no-navbar
-    .content:not(.custom) > h1, h2, h3, h4, h5, h6
-        margin-top 1.5rem
-        padding-top 0
+    {$contentClass}:not(.custom) > h1, h2, h3, h4, h5, h6
+      margin-top 1.5rem
+      padding-top 0
+
     .sidebar
       top 0
 
@@ -180,6 +195,7 @@ th, td
   .theme-container.no-sidebar
     .sidebar
       display none
+
     .page
       padding-left 0