Remove rounded corners, Raspbian Jessie pixel

I just installed OpenBox configuration tool to remove visual effects from raspbian operating system:

sudo apt-get install obconf -y

Now when I select different theme I have ugly corners in any kind of window:

Turns out this can be remove by opening:

geany ~/.config/openbox/lxde-pi-rc.xml

Somewhere in line 53 I have to set:

    <roundCorners>no</roundCorners>

Screenshot: