fix: Set 'width' on heading elements to fix flexible element wrapping in Safari

https://github.com/philipwalton/flexbugs#11-min-and-max-size-declarations-are-ignored-when-wrapping-flex-items

Author: smockle

docs/custom.css

@@ -1,6 +1,6 @@
 pre { font-size: 100% !important }
 code { font-size: 90% !important }
 
-h1, h2, h3, h4, h5 { margin: 1rem 0 }
+h1, h2, h3, h4, h5 { margin: 1rem 0; width: 100%; }
 ul li { margin-left: 1rem }