[libc] Website fixes (sidebar and mobile)

Add "using" and "status" sections to the sidebar to make getting these
easier.

Fixed mobile formatting not overflow left and right.

Tested:
Chrome on Desktop, using mobile restrictions in devtools.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D131369

libc/docs/_static/custom.css

@@ -6,10 +6,6 @@ div.document {
   width: 90%;
 }
 
-div.body {
-  max-width: 90%;
-}
-
 div.note {
   padding: 20px 20px 10px 20px;
 }
@@ -98,3 +94,21 @@ div.sphinxsidebar h3 {
   /* Hide Navigation. */
   display: none;
 }
+
+@media screen and (min-width: 875px) {
+div.body {
+  max-width: 90%;
+}
+}
+
+@media screen and (max-width: 875px) {
+div.sphinxsidebar {
+  margin-left: 0px;
+  margin-right: 0px;
+}
+
+div.body {
+  min-width: auto;
+  max-width: auto;
+}
+}

libc/docs/index.rst

@@ -47,7 +47,23 @@ stages there is no ABI stability in any form.
 .. toctree::
    :hidden:
    :maxdepth: 1
-   :caption: Documentation
+   :caption: Using
+
+   runtimes_build
+
+.. toctree::
+   :hidden:
+   :maxdepth: 1
+   :caption: Status
+
+   strings
+   stdio
+   math
+
+.. toctree::
+   :hidden:
+   :maxdepth: 1
+   :caption: Development
 
    build_system
    clang_tidy_checks
@@ -61,10 +77,6 @@ stages there is no ABI stability in any form.
    mechanics_of_public_api
    redirectors
    source_layout
-   strings
-   runtimes_build
-   stdio
-   math
 
 .. toctree::
    :hidden:
@@ -72,4 +84,4 @@ stages there is no ABI stability in any form.
    :caption: External Links
 
    Source Code <https://github.com/llvm/llvm-project/tree/main/libc>
-   Bug Reports <https://github.com/llvm/llvm-project/issues/labels/libc/>
+   Bug Reports <https://github.com/llvm/llvm-project/labels/libc>