WeChat Mini Programs Mobile phone Virtual Button and canvas layout problem

<canvas style="width:{{width}}; height: {{height}};" canvas-id="firstCanvas">
  <cover-view class="button_full" bindtap="saveIMG" style="position: fixed; height:50px; padding:0px; line-height:50px; text-align:center; bottom:0px; color:-sharpFFF;"></cover-view>
</canvas>

the page layout is as above, which is normal when the Android virtual button is displayed, but after putting it away, the layout of the Save Picture button has changed. what is the problem?

Css WeChat-Mini-Programs
Mar.18,2021

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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-64f5-1b3ae2b-2c257.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3ae2b-2c257.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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