A city government imposes a proportional income tax on all people who earn income within its city limits. In​ 2004, the​ city's income tax rate was 0.050.05 ​(55 ​percent), and it collected ​$20.0020.00 million in income taxes. In​ 2005, it raised the income tax rate to 0.060.06 ​(66 ​percent), and its income tax collections declined to ​$19.2019.20 million. What happened to the​ city's income tax base between 2004 and​ 2005?