Why do I add height, to other parts to make the overflow:auto of adjacent parts work?

at first I didn"t write the CSS and HTML of the main area
the following code is the sidebar CSS, page effect as shown in figure 2
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main

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Mar.06,2021
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-64f5-1b334e0-2be67.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b334e0-2be67.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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