docs: Fix background color for interactive examples

For the few weird code blocks where default highlighting does not work,
we must add the 'highlight' class manually to get matching backgrounds.
This reuses the background color defined in pygments.css.

doc_src/tutorial.rst

@@ -92,6 +92,7 @@ Syntax Highlighting
 You'll quickly notice that fish performs syntax highlighting as you type. Invalid commands are colored red by default:
 
 .. parsed-literal::
+    :class: highlight
 
     :prompt:`>` :red:`/bin/mkd`
 
@@ -103,6 +104,7 @@ A command may be invalid because it does not exist, or refers to a file that you
 Valid file paths are underlined as you type them:
 
 .. parsed-literal::
+    :class: highlight
 
     :prompt:`>` :command:`cat` :param-valid-path:`~/somefi`
 
@@ -169,6 +171,7 @@ Autosuggestions
 As you type fish will suggest commands to the right of the cursor, in gray. For example:
 
 .. parsed-literal::
+    :class: highlight
 
     :prompt:`>` :red:`/bin/h`:gray:`ostname`
 
@@ -176,6 +179,7 @@ As you type fish will suggest commands to the right of the cursor, in gray. For
 It knows about paths and options:
 
 .. parsed-literal::
+    :class: highlight
 
     :prompt:`>` :command:`grep` :param:`--i`:gray:`gnore-case`
 
@@ -183,6 +187,7 @@ It knows about paths and options:
 And history too. Type a command once, and you can re-summon it by just typing a few letters:
 
 .. parsed-literal::
+    :class: highlight
 
     :prompt:`>` :red:`r`:gray:`sync -avze ssh . myname@somelonghost.com:/some/long/path/doo/dee/doo/dee/doo`
 
@@ -197,6 +202,7 @@ A rich set of tab completions work "out of the box".
 Press :kbd:`Tab` and fish will attempt to complete the command, argument, or path:
 
 .. parsed-literal::
+    :class: highlight
 
     :prompt:`>` :red:`/pri`:kbd:`Tab` => :command:`/private/`
 
@@ -204,6 +210,7 @@ Press :kbd:`Tab` and fish will attempt to complete the command, argument, or pat
 If there's more than one possibility, it will list them:
 
 .. parsed-literal::
+    :class: highlight
 
     :prompt:`>` :red:`~/stuff/s`:kbd:`Tab`
     ~/stuff/script.sh  (Executable, 4.8kB)  ~/stuff/sources/  (Directory)
@@ -214,6 +221,7 @@ Hit tab again to cycle through the possibilities.
 fish can also complete many commands, like git branches:
 
 .. parsed-literal::
+    :class: highlight
 
     :prompt:`>` :command:`git` :param:`merge pr`:kbd:`Tab` => :command:`git` :param:`merge prompt_designer`
     :prompt:`>` :command:`git` :param:`checkout b`:kbd:`Tab`
@@ -599,6 +607,7 @@ Unlike other shells, there is no prompt variable like ``PS1``. To display your p
 You can define your own prompt from the command line:
 
 .. parsed-literal::
+    :class: highlight
 
     > function fish_prompt; echo "New Prompt % "; end
     New Prompt % _
@@ -619,6 +628,7 @@ Multiple lines are OK. Colors can be set via :ref:`set_color <cmd-set_color>`, p
 This prompt would look like:
 
 .. parsed-literal::
+    :class: highlight
 
     :purple:`02/06/13`
     :red:`/home/tutorial >` _