The web page that created bootstrap in idea does not take effect.

problem description

Python flask"s web project, which I created in idea, creates an index.html, that references the bootstrap, of the local directory but does not take effect.

the path in href is OK if you enter the absolute path, but the relative path is not correct. Is there something wrong?
my code structure and directory are shown in the screenshot. Please give us some suggestions:
Picture description

Html python bootstrap
Oct.25,2021

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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-64f5-1ea95f8-1f4c.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1ea95f8-1f4c.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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