Para openSUSE Leap 15.4 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/Documentation:Tools/openSUSE_Leap_15.4/Documentation:Tools.repo
zypper refresh
zypper install docbook5-xsl-stylesheets
Para SLE 15 SP5 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/Documentation:Tools/SLE_15_SP5/Documentation:Tools.repo
zypper refresh
zypper install docbook5-xsl-stylesheets
Para SLE 15 SP4 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/Documentation:Tools/SLE_15_SP4/Documentation:Tools.repo
zypper refresh
zypper install docbook5-xsl-stylesheets
Para SLE 15 SP3 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/Documentation:Tools/SLE_15_SP3/Documentation:Tools.repo
zypper refresh
zypper install docbook5-xsl-stylesheets
Para SLE 12 SP5 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/Documentation:Tools/SLE_12_SP5/Documentation:Tools.repo
zypper refresh
zypper install docbook5-xsl-stylesheets