CSS issue displaying resizer with resizable layouts.
With git version (3.3.0-rc4-1-g9536c9f), there seems to be an issue displaying the resizers for resizable layouts (only tested with WHBoxLayout) in both the polished theme and the bootstrap theme. Tested using Chromium Version 25.0.1364.160 Debian 7.0 (186726). The resizer (div.Wt-vrh2) is displayed with a transparent background color rather than #EEEEEE (which appears to be the intent).
The attached patch seemed to fix the issue in my testing. NOTE: I only tested the horizontal layout for the polished and bootstrap themes.