Fix Sass deprecation warning
Fix Sass deprecation warning

```
DEPRECATION WARNING: Using / for division is deprecated and will be removed in Dart Sass 2.0.0.

Recommendation: math.div($size, 2)

More info and automated migrator: https://sass-lang.com/d/slash-div

  ╷
7 │     border-width: $size / 2;
```
NightCatSama/vue-slider-component,NightCatSama/vue-slider-component,NightCatSama/vue-slider-component,NightCatSama/vue-slider-component