Fix dark css rule

[GuillaumeGomez]

Fixes #59817.

r? @rust-lang/rustdoc

[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

travis_time:end:033b22db:start=1554836944518034636,finish=1554837030288527768,duration=85770493132
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
$ export GCP_CACHE_BUCKET=rust-lang-ci-cache
$ export AWS_ACCESS_KEY_ID=AKIA46X5W6CZEJZ6XT55
---
travis_time:start:test_assembly
Check compiletest suite=assembly mode=assembly (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:13:33] 
[01:13:33] running 9 tests
[01:13:33] iiiiiiiii
[01:13:33] 
[01:13:33]  finished in 0.156
[01:13:33] travis_fold:end:test_assembly

---
travis_time:start:test_debuginfo
Check compiletest suite=debuginfo mode=debuginfo-both (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:13:50] 
[01:13:50] running 121 tests
[01:14:18] .iiiii...i.....i..i...i..i.i.i..i.ii...i.....i..i....i..........iiii..........i...ii...i.......ii.i. 100/121
[01:14:23] i.i......iii.i.....ii
[01:14:23] 
[01:14:23]  finished in 33.779
[01:14:23] travis_fold:end:test_debuginfo

---
[01:43:44] travis_time:end:stage0-rustdoc-themes:start=1554843262683959351,finish=1554843263693558282,duration=1009598931

[01:43:44] rustdoc: [theme-checker] Starting tests!
[01:43:44]  - Checking "/checkout/src/librustdoc/html/static/themes/dark.css"... FAILED
[01:43:44]   Missing ".stab > code" rule
[01:43:44] 
[01:43:44] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/rustdoc-themes" "/checkout/obj/build/bootstrap/debug/rustdoc" "/checkout/src/librustdoc/html/static/themes"
[01:43:44] expected success, got: exit code: 1
[01:43:44] 
[01:43:44] 
[01:43:44] 
[01:43:44] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:43:44] Build completed unsuccessfully in 0:42:42
[01:43:44] Makefile:48: recipe for target 'check' failed
[01:43:44] make: *** [check] Error 1
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:1513f6cc
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Tue Apr  9 20:54:24 UTC 2019
---
travis_time:end:091bab24:start=1554843266463418512,finish=1554843266468398546,duration=4980034
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:125f3026
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:047cbe60
travis_time:start:047cbe60
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:14e3ad6e
$ dmesg | grep -i kill

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[tesuji]

r? @QuietMisdreavus, this PR is looking for your review.

[GuillaumeGomez]

This is a fix and a short one, it'd be nice to be have it merged as quickly as possible.

r? @Manishearth

[Manishearth]

@bors r+ rollup

[bors]

📌 Commit 0e6049a has been approved by Manishearth