doc: css: improve C constructs spacing

With current CSS construct like void f() are rendered together, i.e.
voidf(). Add some spacing to make it more like "void f()".

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
diff --git a/doc/_static/css/custom.css b/doc/_static/css/custom.css
index 9d2b5c9..b3368b5 100644
--- a/doc/_static/css/custom.css
+++ b/doc/_static/css/custom.css
@@ -171,6 +171,12 @@
     padding: 0 4px !important;
 }
 .rst-content dl:not(.docutils) .sig-param,
+.rst-content dl:not(.docutils).class dt > code,
+.rst-content dl:not(.docutils).function dt > code,
+.rst-content dl:not(.docutils).method dt > code {
+    padding: 0 4px !important;
+}
+.rst-content dl:not(.docutils) .sig-param,
 .rst-content dl:not(.docutils).class dt > .optional ~ em,
 .rst-content dl:not(.docutils).function dt > .optional ~ em,
 .rst-content dl:not(.docutils).method dt > .optional ~ em {
@@ -899,6 +905,14 @@
     border-left: none !important;
 }
 
+.rst-content dl:not(.docutils).c.var .pre {
+  padding-right: 4px;
+}
+
+.rst-content dl:not(.docutils).c.struct .property {
+  padding-right: 4px !important;
+}
+
 /* Misc tweaks */
 
 .rst-columns {