code: function resizeMixin(decl, i) {
    if (decl.prop == 'resize' && decl.value !== 'none') {
      var count = 0
      decl.parent.walkDecls(function(decl) {
        if (decl.prop == 'overflow') count++
      })
      if (count === 0) {
        var reBefore = decl.raws.before.replace(reBLANK_LINE, '$1')
  
        insertDecl(decl, i, {
          raws: {
            before: reBefore
          },
          prop: 'overflow',
          value: 'auto'
        })
      }
    }
  }
docs: resize mixin
  resize 只有在 overflow 不为 visible 时生效