VUX version

2.9.0

OS/Browsers version

any

Vue version

2.5.17-beta.0

Code

``css
@cell-default-arrow-width: 16px;

//weui-access.less 第 9 行 .weui-cell__ft 的代码，这里有问题：

.weui-cell__ft {
    padding-right: 13px;
    position: relative;
    &:after {
        content: " ";
        .setArrow(right, @cell-default-arrow-width, @cell-default-arrow-color, @cell-default-arrow-border-width);
        position: absolute;
        top: 50%;
        margin-top: -4px;
        right: 2px;
    }
}

//------------------------------------------------------
//既然箭头可以通过 @cell-default-arrow-width 设置尺寸， 那top 和margin-top 就不应该写死。

### Steps to reproduce

设置 cell-default-arrow-width 设置箭头大小。

### What is Expected?

设置 cell-default-arrow-width 后，箭头还能保持上下居中

### What is actually happening?

设置 cell-default-arrow-width 后，箭头不能上下居中

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