Why does the document type invalidate the css style?

header declaration

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" >

Why do some css styles fail?

after changing to html5 returned to normal.

Doctype css javascript html

Oct.26,2021

some styles do not conform to the DTD XHTML 1.0 Strict standard

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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-64f5-1b3707b-410a0.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3707b-410a0.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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