The influence of webpack4 tree shaking on css

what is the side effect code? does CSS count? why can"t css be packaged after using tree shake? it is necessary to configure siderEffect to package css files

Apr.28,2021
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b3dcf8-2c3a4.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3dcf8-2c3a4.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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