SVG does not respect overflow:visible.

Source/core/css/svg.css

 /*
  * The default style sheet used to render SVG.
  *
  * Copyright (C) 2005, 2006 Apple Computer, Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 29 matching lines @@
     the initial clipping path is set according to the clipping rules as defined in [CSS2-overflow].
 
     Opera/Firefox & WebKit agreed on NOT setting "overflow: hidden" for the outermost svg element - SVG 1.1 Errata
     contains these changes as well as all future SVG specifications: see http://lists.w3.org/Archives/Public/public-svg-wg/2008JulSep/0347.html
 */
 
 svg:not(:root), symbol, image, marker, pattern, foreignObject {
     overflow: hidden
 }
 
+svg:root {
+    overflow: hidden;

[krit, 2014/04/01 12:23:14]

It of course depends how the spec defines the svg root element, but it says:

""
The initial value for ‘overflow’ as defined in [CSS2-overflow] is 'visible', and
this applies also to the root ‘svg’ element; however, for child elements of an
SVG document, SVG's user agent style sheet overrides this initial value and sets
the ‘overflow’ property on elements that establish new viewports (e.g., ‘svg’
elements), ‘pattern’ elements and ‘marker’ elements to the value 'hidden'.
""

So for all SVG root elements, the value should be visible, not hidden. For all
child elements establishing a viewport the UA style sheet should be hidden.
According to the spec, this edit is wrong.

+}
+
 text, foreignObject {
     display: block
 }
 
 text {
    white-space: nowrap
 }
 
 tspan, textPath {
    white-space: inherit
 }
 
 /* states */
 
 :focus {
     outline: auto 5px -webkit-focus-ring-color
 }
 
 /* CSS transform specification: "transform-origin 0 0 for SVG elements without associated CSS layout box, 50% 50% for all other elements". */
  
 * {
     -webkit-transform-origin: 0 0;
 }
 
 html|* > svg {
     -webkit-transform-origin: 50% 50%;
 }