diff --git a/engine/compresscss.sh b/engine/compresscss.sh
index 763a779..3c4670f 100755
--- a/engine/compresscss.sh
+++ b/engine/compresscss.sh
@@ -1,7 +1,8 @@
 #!/usr/bin/env nix-shell
+#!nix-shell --pure
 #!nix-shell -i bash
 #!nix-shell -I nixpkgs="https://github.com/NixOS/nixpkgs/archive/19.09.tar.gz"
-#!nix-shell -p minify
+#!nix-shell -p bash minify
 
 # nix-shell -p nodePackages.clean-css
 
diff --git a/src/css/y.css b/src/css/y.css
index 7fb425a..a3f61fe 100644
--- a/src/css/y.css
+++ b/src/css/y.css
@@ -112,7 +112,7 @@ html {
 }
 
 body {
-  font-family: "American Typewriter", Georgia, Cambria, 'Times New Roman', Times, serif;
+  font-family: "American Typewriter", Georgia, serif;
   line-height: 1.5;
 
   max-width: 60ch;
@@ -125,7 +125,7 @@ body {
   counter-reset: definition;
 
   color: hsl(0, 5%, 10%);
-  background-color: hsl(210, 20%, 98%);
+  background-color: hsl(218, 20%, 98%);
 
   text-rendering: optimizeLegibility;
 }
@@ -144,12 +144,6 @@ a:not([class]) {
   text-decoration-skip-ink: auto;
 }
 
-/* Make links red */
-a,
-a:visited {
-  color: #a00;
-}
-
 /* Make images easier to work with */
 img {
   max-width: 100%;
@@ -181,12 +175,12 @@ kbd {
   font-family: Courier, monospace;
 }
 pre {
-  padding: 1rem 1.4rem;
+  padding: 1rem;
   max-width: 100%;
   overflow: auto;
-  border: 1px solid hsl(210, 15%, 49%);
+  border: 1px solid hsl(218, 15%, 49%);
   border-radius: 4px;
-  background: hsl(210, 40%, 96%);
+  background: hsl(218, 40%, 96%);
   font-size: 85%;
 }
 pre code {
@@ -194,8 +188,8 @@ pre code {
   position: relative;
 }
 kbd {
-  background: hsl(210, 5%, 100%);
-  border: 1px solid hsl(210, 5%, 70%);
+  background: hsl(218, 5%, 100%);
+  border: 1px solid hsl(218, 5%, 70%);
   border-radius: 2px;
   padding: 2px 4px;
   font-size: 75%;
@@ -238,8 +232,9 @@ nav li {
 }
 
 /* Center definitions (most useful for display equations) */
+dl dt { font-weight: 700; }
 dl dd {
-  text-align: center;
+  padding-left: 3rem;
 }
 
 /* Theorem */
@@ -414,6 +409,8 @@ body>input { display: none; }
 #labels > .content { margin: 0 auto; text-align: center; }
 label { font-weight: 700; }
 label:hover { cursor: pointer; }
+label ~ pre { margin-top: 0; }
+.org-src-container { margin: 1rem 0; }
 #logo { text-align: center; }
 body { margin:0; padding: 0; border: 0; max-width: none;}
 #preamble, #postamble { text-align: center; }
@@ -426,7 +423,13 @@ figure img { width: 100%; }
 .footdef > sup { vertical-align: top; font-size: medium; }
 .footdef > sup > a { padding: 0.5em; }
 .footpara { display: inline; }
-footer { margin: 3em 0; padding: 1em 0; border-top: solid 1px; border-bottom: solid 1px; line-height: 1em; }
+footer { margin: 3em 0;
+         padding: 1em 0;
+         border-top: solid 1px;
+         border-bottom: solid 1px;
+         line-height: 1em;
+         font-size: 0.85em;
+       }
 td { border-bottom: none; padding: .2rem; }
 table { margin-top: 1rem; }
 nav { text-align: center; padding: 2em 0;  }
@@ -458,24 +461,32 @@ pre { line-height: 1em; }
     --fg0: var(--b0);
     --fg: var(--b02);
     --rfg: #000;
-    --hl: var(--o);
+    --hl: var(--r);
 }
 
 /* dark preferred */
 @media (prefers-color-scheme: dark)
 {
     :root {
-        --bg: hsl(210,20%,11%);
+        --bg: hsl(218,20%,16%);
         --rbg: var(--b03);
-        --fg: var(--b1);
+        --fg: var(--b0);
         --fg0: var(--b00);
         --rfg: var(--b2);
         --hl: var(--g);
+        --y: #ae8c51;
+        --o: #a9654a;
+        --r: #af6255;
+        --m: #ae5e7d;
+        --v: #6774b2;
+        --b: #3f8cc3;
+        --c: #15a198;
+        --g: #939452;
     }
     img { filter: brightness(0.7) saturate(0.5); }
     pre {
-        background: hsl(210,40%,15%);
-        border-color: hsl(210,15%,43%);
+        background: hsl(218,20%,18%);
+        border-color: hsl(218,15%,23%);
     }
 }
 
@@ -487,30 +498,53 @@ input#l:checked ~ div {
     --fg: var(--b02);
     --rfg: #000;
     --hl: var(--o);
+    --y: #c18600;
+    --o: #d84100;
+    --r: #e62729;
+    --m: #ec0085;
+    --v: #6c71c4;
+    --b: #0095ff;
+    --c: #00b0a3;
+    --g: #879a00;
 }
 input#l:checked ~ div img {
     filter: none;
 }
 input#l:checked ~ div pre {
-    border: 1px solid hsl(210, 15%, 49%);
-    background: hsl(210, 40%, 96%);
+    border: 1px solid hsl(218, 15%, 49%);
+    background: hsl(218, 40%, 96%);
 }
 
 /* dark checked */
 input#d:checked ~ div {
-    --bg: hsl(210,20%,11%);
+    --bg: hsl(218,20%,16%);
     --rbg: var(--b03);
-    --fg: var(--b1);
+    --fg: var(--b0);
     --fg0: var(--b00);
     --rfg: var(--b2);
     --hl: var(--g);
+    --y: #ae8c51;
+    --o: #a9654a;
+    --r: #af6255;
+    --m: #ae5e7d;
+    --v: #6774b2;
+    --b: #3f8cc3;
+    --c: #15a198;
+    --g: #939452;
 }
 input#d:checked ~ div img {
     filter: brightness(0.7) saturate(0.5);
 }
 input#d:checked ~ div pre {
-    background: hsl(210,40%,15%);
-    border-color: hsl(210,15%,43%);
+    background: hsl(218,20%,18%);
+    border-color: hsl(218,15%,23%);
+}
+
+/* ---- */
+::selection {
+    background: var(--m);
+    color: hsl(218,40%,96%);
+    text-decoration: hsl(218,40%,96%);
 }
 
 body, body > div {
diff --git a/src/drafts/XXXX-how-i-use-nix/index.org b/src/drafts/XXXX-how-i-use-nix/index.org
index 1715512..329a98a 100644
--- a/src/drafts/XXXX-how-i-use-nix/index.org
+++ b/src/drafts/XXXX-how-i-use-nix/index.org
@@ -11,118 +11,163 @@
 #+OPTIONS: H:5 auto-id:t toc:nil
 #+STARTUP: showeverything
 
-In this article I'll explain how I use nix.
-I don't use NixOS nor any Linux as my main desktop environment[fn:desktop].
-Still I use [[https://nixos.org/nix][nix]] on a few mac computers.
-It has multiple usages.
+Have you ever written a small script and you update your system and this
+stop working?
+Have you copied your tool/script to another machine it doesn't work because
+some dependency is missing?
+Have you tried to sync your dotfiles to another env and there are a few
+details not working? Some missing dependency?
+If the answer is yes, then [[https://nixos.org/nix][nix]] can help.
 
-First, let's start by the bad news.
-Recent macOS security policy made nix a bit harder to install on a mac.
-See [[https://hydra.nixos.org/build/119559243/download/1/manual/#sect-macos-installation][macOS Installation instructions]].
+** Scripts
+:PROPERTIES:
+:CUSTOM_ID: scripts
+:END:
 
-Once you have nix installed you should update the nix-channel.
-Mainly a nix-channels is where are the definitions of all the packages.
-See [[https://hydra.nixos.org/build/119559243/download/1/manual/#sec-channels][nixOS documentation]].
+Suppose you want to write a portable script.
+For example, the script I use to minify my CSS.
+Here it is:
+
+#+begin_src shell
+#!/usr/bin/env nix-shell
+#!nix-shell --pure
+#!nix-shell -i bash
+#!nix-shell -I nixpkgs="https://github.com/NixOS/nixpkgs/archive/19.09.tar.gz"
+#!nix-shell -p bash minify
+
+minify "$1" > "$2"
+#+end_src
+
+So let's analyze each line of the header block:
+
+- ~#!/usr/bin/env nix-shell~ :: basic, use ~nix-shell~ to run the script.
+- ~#!nix-shell --pure~ :: only use dependencies installed in this nix shell
+  environment. A bit as if the PATH environment variable was emptied.
+- ~#!nix-shell -i bash~ :: tell ~nix-shell~ to run ~bash~
+- ~#!nix-shell -I nixpkgs="https://github.com/NixOS/nixpkgs/archive/19.09.tar.gz"~ ::
+  pin the nixpkgs using this archive.
+- ~#!nix-shell -p bash minify~ :: install ~bash~ and ~minify~ in the nix shell.
+
+Now if the script is run on a machine with ~nix~ installed you can be
+pretty sure it will work as expected.
+Even if I update my OS and I forget about this script for a few years.
+As long as I can install nix on the new system and I could download the tar
+file the script will be run the same way as the day I wrote it.
+
+** Temporary working env
+:PROPERTIES:
+:CUSTOM_ID: temporary-working-env
+:END:
+
+Quite often, I need to do something, and run a specific command that need
+me to install a very specific command.
+And I'm pretty sure I will not use this tool ever again.
+
+For those cases, what I do, is generally run my command directly with a
+fresh ~nix-shell~.
+
+#+begin_src shell
+> nix-shell -p httpie
+[nix-shell:~]$ ... here I can use httpie ...
+#+end_src
 
 ** Home Manager
 :PROPERTIES:
 :CUSTOM_ID: home-manager
 :END:
 
-First, I use [[https://github.com/rycee/home-manager][home-manager]], it's first usage it to list a reproductible list
-of application I need on all my desktop environments.
-So i edit the file =~/.config/nixpkgs/home.nix=.
-I provide a list of packages I want to have when I start a new shell.
+A few years ago I used =brew= to install the tools I need.
+With =nix= you can install a new tool with ~nix-env -i~ instead of ~brew install~.
+Still recently I prefer to use [[https://github.com/rycee/home-manager][home-manager]].
 
+The main advantage is that it is even more reproductible and can easily be
+shared accross different machines.
+
+Mainly when I need a new binary I add it in a description list in the file
+=~/.config/nixpkgs/home.nix=.
+It looks like this:
 
 #+begin_src nix
-  home.packages = with pkgs; [
-    # nix
-    nix-prefetch-git
-    lorri
-    # emacs
-    emacsMacport
-    imagemagick
-    gnupg
-    # vim
-    neovim
-    # shell
-    direnv
-    fasd
-    fd
-    findutils
-    fortune
-    gawk
-    git
-    gitAndTools.diff-so-fancy
-    graphviz
-    htop
-    httpie
-    jq
-    jwt-cli
-    libressl
-    mustache-go
-    pandoc
-    ripgrep
-    rtv
-    wakatime
-    xpdf # pdftotext
-    yadm
-    youtube-dl
-    # clojure
-    leiningen
-    boot
-    adoptopenjdk-bin
-    joker
-    # Haskell
-    ghc
-    cabal-install
-    (all-hies.selection
-      { selector = p:
-          { inherit (p) ghc865; };})
-    # Common LISP
-    sbcl
-    # mails
-    offlineimap
-    notmuch
-    msmtp
-    gmailieer
-    # docker
-    docker-compose
-    # weechat
-    rel20weechat
-    aspell
-    aspellDicts.en
-    aspellDicts.fr
-  ];
+home.packages = with pkgs; [
+  # emacs
+  emacsMacport
+  imagemagick
+  gnupg
+  # shell
+  direnv
+  ...
+];
 #+end_src
 
+then I simply run ~home-manager switch~ and I've got all those tools in my env.
+
+*** Pinning the packages
+:PROPERTIES:
+:CUSTOM_ID: pinning-the-packages
+:END:
+
+#+begin_src nix
+{ config, pkgs, ... }:
+let
+  # ...
+  pkgs = import (fetchGit {
+    name = "nixpkgs20";
+    url = "https://github.com/NixOS/nixpkgs";
+    # obtained via
+    # git ls-remote https://github.com/NixOS/nixpkgs nixpkgs-20.03-darwin
+    ref = "refs/heads/nixpkgs-20.03-darwin";
+    rev = "58f884cd3d89f47672e649c6edfb2382d4afff6a";
+  }) {};
+  # ...
+in {
+  # ...
+}
+#+end_src
+
+*** Specific tools
+:PROPERTIES:
+:CUSTOM_ID: specific-tools
+:END:
+
 There are a few noticiable artifact here:
 
-The first one is ~rel20weechat~ is a very specify build of weechat with the
+The first one is ~weechat~ is a very specify build of weechat with the
 plugin I need. So here is the block I use:
 
 #+begin_src nix
-rel20 = import (fetchGit {
-  name = "nixpkgs20";
-  url = "https://github.com/NixOS/nixpkgs";
-  # obtained via
-  # git ls-remote https://github.com/NixOS/nixpkgs nixpkgs-20.03-darwin
-  ref = "refs/heads/nixpkgs-20.03-darwin";
-  rev = "58f884cd3d89f47672e649c6edfb2382d4afff6a";
-}) {};
-rel20weechat = rel20.weechat.override {
-    configure = { availablePlugins, ... }: {
-      # plugins = with availablePlugins; [ python perl guile ];
-      scripts = with pkgs.weechatScripts; [ wee-slack ];
+let
+  ...
+  rel20weechat = rel20.weechat.override {
+      configure = { availablePlugins, ... }: {
+        # plugins = with availablePlugins; [ python perl guile ];
+        scripts = with pkgs.weechatScripts; [ wee-slack ];
+      };
     };
-  };
+  ...
+in
+{
+  ...
+  home.packages = with pkgs; [... rel20weechat ...];
+  ...
+}
 #+end_src
 
 First ~rel20~ pin a nixpkgs some specific commit of nix packages.
 Second, I overriden the default packages of the =weechat= package.
 
-Another interresting one is this block:
+*** Another nice tool is =sws=
+:PROPERTIES:
+:CUSTOM_ID: another-nice-tool-is--sws-
+:END:
+
+I use macOS so even though I'm using a darwin focused nixpkgs
+sometimes a few package can be broken and can't be installed.
+
+
+That occurred with [[https://hackage.haskell.org/package/sws][=sws=]] during the upgrade to 20.03 on darwin.
+This is a simple tool that need haskell to be compiled locally and
+installed.
+Here is how I could install it:
 
 #+begin_src nix
 let
@@ -133,46 +178,35 @@ let
     ref = "refs/heads/nixpkgs-19.09-darwin";
     rev = "2f9bafaca90acd010cccd0e79e5f27aa7537957e";
   }) {};
-  haskellDeps = ps: with ps; [
-    base
-    protolude
-    tidal
-    shake
-    rel19.haskellPackages.sws
-    ];
-  ghc = pkgs.haskellPackages.ghcWithPackages haskellDeps;
   ...
 in
   home.packages = with pkgs; [
     ...
     ghc
+    rel19.haskellPackages.sws
     ...
   ]
 #+end_src
 
-So it means I want to install =ghc= the main Haskell compiler.
-But also with some specific haskell packages.
-The interresting part, is that in most classical OS environment if you want
-a package from a specific language platform.
-You need to install the package manager for this language (npm, pip,
-etc...).
-And in =nixpkgs= there are formulae for most of these language specific
-packages.
-So instead of just installing =cabal-install= and then installing the
-packages I need.
-Which could also go bad, because they might be upgraded and not be
-compatible all at the same time.
-
-I used nix to install the packages I needed.
-And one interresting detail.
-One package [[https://hackage.haskell.org/package/sws][=sws=]] is broken in 20.03 on darwin.
 So I used the older version from 19.09.
 
 [fn:desktop]: I'm using macOS, and I have multiple macs.
 A laptop and two desktop machines.
-Using the 27" iMac is my ultimate work station.
+Using the 27″ iMac is my ultimate work station.
 It really enhance my productivity.
 Still the laptop is a superior work environment for more casual tasks.
 I guess I might write someday about my full work environment.
 
+** Install
+:PROPERTIES:
+:CUSTOM_ID: install
+:END:
+
+First, let's start by the bad news.
+Recent macOS security policy made nix a bit harder to install on a mac.
+See [[https://hydra.nixos.org/build/119559243/download/1/manual/#sect-macos-installation][macOS Installation instructions]].
+
+Once you have nix installed you should update the nix-channel.
+Mainly a nix-channels is where are the definitions of all the packages.
+See [[https://hydra.nixos.org/build/119559243/download/1/manual/#sec-channels][nixOS documentation]].