To use the simply type percent (xs:decimal), see the snippet below.
<xs:simpleType name="percent">
<xs:annotation>
<xs:documentation>The percent type specifies a value from 0 to 100.</xs:documentation>
</xs:annotation>
<xs:restriction base="xs:decimal">
<xs:minInclusive value="0"/>
<xs:maxInclusive value="100"/>
</xs:restriction>
</xs:simpleType>