Install this package:
emerge -a lxde-base/lxde-icon-theme
If the package is masked, you can unmask it using the autounmask tool or standard emerge options:
autounmask
emerge
autounmask lxde-base/lxde-icon-theme
Or alternatively:
emerge --autounmask-write -a lxde-base/lxde-icon-theme
<pkgmetadata> <upstream> <remote-id type="sourceforge">lxde</remote-id> </upstream> </pkgmetadata>