Centralize base styles for docs.bazel.build using bazel-website's css

The base style.scss is already identical between the two sites; this PR pulls it from bazel-website instead of having a local copy.

Like https://github.com/bazelbuild/bazel-blog/pull/225, but for docs.bazel.build

For bazelbuild/bazel#10793

Closes #11376.

PiperOrigin-RevId: 311500094
diff --git a/WORKSPACE b/WORKSPACE
index 7a65056..0ab394d 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -567,6 +567,7 @@
 
 load("//scripts/docs:doc_versions.bzl", "DOC_VERSIONS")
 
+# Load versioned documentation tarballs from GCS
 [http_file(
     # Split on "-" to get the version without cherrypick commits.
     name = "jekyll_tree_%s" % DOC_VERSION["version"].split("-")[0].replace(".", "_"),
@@ -574,6 +575,20 @@
     urls = ["https://mirror.bazel.build/bazel_versioned_docs/jekyll-tree-%s.tar" % DOC_VERSION["version"]],
 ) for DOC_VERSION in DOC_VERSIONS]
 
+# Load shared base CSS theme from bazelbuild/bazel-website
+http_archive(
+    name = "bazel_website",
+    urls = ["https://github.com/bazelbuild/bazel-website/archive/c174fa288aa079b68416d2ce2cc97268fa172f42.tar.gz"],
+    strip_prefix = "bazel-website-c174fa288aa079b68416d2ce2cc97268fa172f42",
+    sha256 = "a5f531dd1d62e6947dcfc279656ffc2fdf6f447c163914c5eabf7961b4cb6eb4",
+    # TODO(https://github.com/bazelbuild/bazel/issues/10793)
+    # - Export files from bazel-website's BUILD, instead of doing it here.
+    # - Share more common stylesheets, like footer and navbar.
+    build_file_content = """
+exports_files(["_sass/style.scss"])
+"""
+)
+
 # Skydoc recommends declaring its dependencies via "*_dependencies" functions.
 # This requires that the repositories these functions come from need to be
 # fetched unconditionally for everything (including just building bazel!), so
@@ -907,4 +922,3 @@
 
 load("//tools/distributions/debian:deps.bzl", "debian_deps")
 debian_deps()
-
diff --git a/site/BUILD b/site/BUILD
index 000d617..603de25 100644
--- a/site/BUILD
+++ b/site/BUILD
@@ -28,6 +28,15 @@
     visibility = ["//:__pkg__"],
 )
 
+# Required to move the shared CSS Files from the external repo's execroot location
+# to the _sass location expected by the local css/main.scss imports.
+genrule(
+    name = "style-common",
+    srcs = ["@bazel_website//:_sass/style.scss"],
+    outs = ["_sass/style.scss"],
+    cmd = "cp $< $@",
+)
+
 filegroup(
     name = "jekyll-srcs",
     srcs = glob(
@@ -40,7 +49,9 @@
             "command-line-reference-suffix.html",
             "site/README.md",
         ] + DOT_GRAPH_HTML_FILES,
-    ),
+    ) + [
+        ":style-common",
+    ],
 )
 
 pkg_tar(
diff --git a/site/_sass/style.scss b/site/_sass/style.scss
deleted file mode 100644
index 80f1a65..0000000
--- a/site/_sass/style.scss
+++ /dev/null
@@ -1,246 +0,0 @@
-// Heading sizes
-
-$font-size-base: 14px !default;
-
-$h1-font-size: $font-size-base * 2.25 !default;
-$h2-font-size: $font-size-base * 2 !default;
-$h3-font-size: $font-size-base * 1.5 !default;
-$h4-font-size: $font-size-base * 1.35 !default;
-$h5-font-size: $font-size-base * 1.15 !default;
-$h6-font-size: $font-size-base !default;
-
-// Font weights
-
-$font-weight-light: 300 !default;
-$font-weight-normal: 400 !default;
-$font-weight-medium: 500 !default;
-$font-weight-bold: 700 !default;
-
-$font-weight-body-text: $font-weight-normal !default;
-$headings-font-weight: $font-weight-medium !default;
-
-// Bazel logo colors
-$bazel-green: #43a047;
-$bazel-green-light: #76d275;
-$bazel-green-dark-left: #00701a;
-$bazel-green-dark-right: #004300;
-$color-on-bazel-green: #fff;
-
-$body-font-family: 'Open Sans', 'Helvetica Neue', Helvetica, Arial,
-                   sans-serif;
-$code-font-family: 'Monaco', 'Source Code Pro', monospace;
-
-$link-color: $bazel-green-dark-left;
-$link-hover-color: lighten($link-color, 20%);
-$well-color: #eee;
-$code-color: #000;
-$text-color: #000;
-
-$vpad: 0px;
-
-$table-bg: #fff;
-$table-cell-padding: 5px;
-$table-border-color: $bazel-green;
-$text-muted: $color-on-bazel-green;
-$line-height-base: 1.5;
-$line-height-computed: 1.5;
-
-html {
-  position: relative;
-  min-height: 100%;
-  font-size: 100%;
-}
-
-body {
-  padding-top: 50px;
-  color: $text-color;
-  font-family: $body-font-family;
-  line-height: $line-height-base;
-}
-
-a {
-  color: $link-color;
-  font-weight: $font-weight-medium;
-
-  &:hover,
-  &:focus {
-    color: $link-hover-color;
-  }
-
-  code {
-    color: $link-color;
-  }
-}
-
-h1,
-h2,
-h3,
-h4,
-h5,
-h6 {
-  color: $text-color;
-  margin-top: 2rem;
-  margin-bottom: 1rem;
-}
-
-h1 code,
-h2 code,
-h3 code,
-h4 code,
-h5 code,
-h6 code {
-  color: $text-color;
-  background: transparent;
-}
-
-h1 {
-  font-size: $h1-font-size;
-  font-weight: $font-weight-bold;
-}
-
-h2 {
-  font-size: $h2-font-size;
-
-  code {
-    font-size: 24px;
-  }
-}
-
-h3 {
-  font-size: $h3-font-size;
-
-  code {
-    font-size: 20px;
-  }
-}
-
-h4 {
-  font-size: $h4-font-size;
-
-  code {
-    font-size: 18px;
-  }
-}
-
-h5 {
-  font-size: $h5-font-size;
-}
-
-h6 {
-  font-size: $h6-font-size;
-}
-
-p,
-li {
-  font-size: $font-size-base;
-  line-height: $line-height-base;
-}
-
-pre {
-  padding: 8px 16px;
-  margin: 8px 0;
-  font-family: $code-font-family;
-  background-color: $well-color;
-  border: 0;
-  font-size: 100%;
-  line-height: 20px;
-  color: $code-color;
-  border-radius: 6px;
-  box-shadow: 1px 1px 5px #aaa;
-}
-
-code {
-  font-family: $code-font-family;
-  font-size: 13px;
-  background-color: $well-color;
-  color: $code-color;
-}
-
-
-// Imitate material design buttons
-.btn-lg {
-  font-size: 14px;
-  text-transform: uppercase;
-}
-
-$md-shadow-1: rgba(0, 0, 0, .14);
-$md-shadow-2: rgba(0, 0, 0, .2);
-$md-shadow-3: rgba(0, 0, 0, .12);
-
-
-@media (min-width: 768px) {
-  .container {
-    width: 100%;
-    max-width: 100%;
-  }
-}
-
-@media (min-width: 992px) {
-  .content {
-    max-width: 85%;
-  }
-}
-
-.content {
-  padding: 40px 10px;
-  p {
-    line-height: 22px;
-    margin-bottom: 1rem;
-  }
-}
-
-.btn-success {
-  border-radius: 2px;
-  box-shadow: 0 2px 2px 0 $md-shadow-1, 0 3px 1px -2px $md-shadow-2, 0 1px 5px 0 $md-shadow-3;
-  border: 0;
-}
-
-.well {
-  background-color: $well-color;
-  border-color: $well-color;
-  box-shadow: none;
-}
-
-// Shared
-.vpad {
-  padding-top: $vpad;
-}
-
-.page-title-bar {
-  background-color: $bazel-green-light;
-  padding-top: 20px;
-  padding-bottom: 20px;
-
-  h1,
-  h2,
-  h3,
-  h4,
-  h5,
-  h6 {
-    margin: 8px 0 4px;
-    color: $color-on-bazel-green;
-  }
-}
-
-.gsc-control-cse {
-  *,
-  *::before,
-  *::after {
-    -webkit-box-sizing: content-box !important;
-    -moz-box-sizing: content-box !important;
-    box-sizing: content-box !important;
-  }
-}
-
-// Used for the Command-line Reference flag anchors. Linkifying the flag name
-// causes it to turn $link-color (green), but we turn it red here to be consistent
-// with the rest of the code block.
-dd > code > a,
-dl > dt > code > a {
-  color: $code-color;
-}
-
-dl > dt {
-  margin-top: 1.5rem;
-  margin-bottom: .5rem;
-}