TIL! as with most languages, css indentifiers can't start with numbers, but you can get around that using backslash-escapes. you'd use these classes like this:

  <div class="35">

this stackoverflow answer has more info (looks like you can use any symbol you want, even spaces and [{}<>&*] !): https://stackoverflow.com/a/27882887/5534735

It means:

    .1{width:5%}
    .3{width:22%}
    .4{width:30%}
    .5{width:40%}
    .2{width:15%}

It's an escape sequence that lets you have non-alphabetic characters to start a CSS selector. See this for more examples:

https://stackoverflow.com/a/35122909/242404

Escapes for "1", "3", "4", "5", and "2".

Probably a workaround for a CSS grammar issue that makes ".1{…}" not parse correctly?