We need this as bootstrap uses it

The validator can't handle this
(w3c/css-validator#111) and the feature is
only a draft (https://www.w3.org/TR/css-variables-1/) but widely
supported.

Author: vmcj

gitlab/webstandard.sh

@@ -82,7 +82,7 @@ if [ "$TEST" = "w3cval" ]; then
     rm -f localhost/domjudge/jury/config/check/phpinfo*
     # We need any value for bs-gutter-x to calculate with in CSS
     for f in $(find ./ -name "style_domjudge.css*"); do
-        sed -i 's/:root {/:root {--bs-gutter-x: 0em;/g' $f
+        sed -i 's/var(--bs-gutter-x)/1em/g' $f
     done
     section_end upstream_problems