/usr/share/themes/Natura/openbox-3/close.xbm is in openbox 3.5.0-2ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | #define close_width 8
#define close_height 8
static unsigned char close_bits[] = {
0xc3, 0xe7, 0x7e, 0x3c, 0x3c, 0x7e, 0xe7, 0xc3 };
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