build: update doc pins, and css for sphinx 4

Author: nedbat

doc/_static/coverage.css

@@ -38,6 +38,20 @@ img.tideliftlogo {
     margin-bottom: 1em;
 }
 
+.sig {
+    font-family: Consolas,"Andale Mono WT","Andale Mono","Lucida Console","Lucida Sans Typewriter","DejaVu Sans Mono","Bitstream Vera Sans Mono","Liberation Mono","Nimbus Mono L",Monaco,"Courier New",Courier,monospace;
+}
+
+.sig-name, .sig-prename {
+    font-size: 1.1em;
+    font-weight: bold;
+    color: black;
+}
+
+.rst-content dl dt.sig {
+    font-weight: inherit;
+}
+
 /* .. parsed-literal:: isn't styled like other <pre> blocks!? */
 
 .rst-content pre.literal-block {

doc/requirements.pip

@@ -5,10 +5,10 @@
 # https://requires.io/github/nedbat/coveragepy/requirements/
 
 doc8==0.8.1
-pyenchant==3.2.0
-sphinx==3.5.4
+pyenchant==3.2.1
+sphinx==4.1.1
 sphinxcontrib-restbuilder==0.3
 sphinxcontrib-spelling==7.2.1
 sphinx_rtd_theme==0.5.2
 sphinx-autobuild==2021.3.14
-sphinx-tabs==2.1.0
+sphinx-tabs==3.1.0