/**
 * CSS with e.g. 'font-size: 75%' makes the HTML unreadable in the default JEditorPane
 * @param key
 * @param value
 * @return 
 */
private static String fixFontSize( Attribute key, String value ) {
    if( "font-size".equals( key.toString() ) && null != value && value.endsWith( "%" ) ) {
        String strPercentage = value.replace( "%", "");
        int percentage = Integer.parseInt( strPercentage );
        if( percentage < 100 ) {
            value = "100%";
        }
    }
    return value;
}
 

@Override
public void addCSSAttribute( MutableAttributeSet attr, Attribute key, String value ) {
    value = fixFontSize( key, value );
    super.addCSSAttribute( attr, key, value );
}
 

@Override
public boolean addCSSAttributeFromHTML( MutableAttributeSet attr, Attribute key, String value ) {
    value = fixFontSize( key, value );
    return super.addCSSAttributeFromHTML( attr, key, value );
}