请问vue2下app.vue 文件onLaunch启动时改变css值

求大神指点一下怎么在vue2下app.vue 文件onLaunch启动时改变 --normal 的色值？
<style lang="scss">

page,view,scroll-view,swiper,swiper-item,movable-area,movable-view,cover-view,cover-image,icon,text,rich-text,progress,button,checkbox-group,checkbox,form,input,label,picker,picker-view,radio-group,radio,slider,switch,textarea,navigator,functional-page-navigator,image,video,camera,live-player,live-pusher,map,canvas,open-data,web-view,ad{box-sizing: border-box;}  
page{word-break: break-all;  

  --normal: #08CDC1;  

  --border: #E1E1E1;  
  --arrow: #999999;  
  --nothing: #AAAAAA;  
  --red: #F35F4B;  
  --blue: #2F5380;  
  --green: #08B266;  
  --yellow: #EB9003;  
  --black: #000000;  
  --darkGray: #666666;  
  --gray: #999999;  
  --ghostWhite: #F2F2F2;  
  --white: #ffffff;  
    --placeholder:#D7D7D7;  
    --bg1: rgba(5,185,174,0.3);  
    --bg2: rgba(5,185,174,0.5);  
    --price: #D91B00;  
}