Code block background inconsistent for long lines with horizontal scrolling

[jxu]

Markdown code block using four spaces:

    #EXTM3U
    #EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=500000,CODECS="avc1.4d002a",RESOLUTION=1526x856,CLOSED-CAPTIONS=NONE
    500000/index.m3u8
    #EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=200000,CODECS="avc1.4d002a",RESOLUTION=762x424,CLOSED-CAPTIONS=NONE
    200000/index.m3u8

Screenshot

The whole div isn't big enough