[css] Do not use duplicate style definitions

[qingtiandalaoye]

in file "app.wxss":

.page__ft{ text-align: center; padding:0 0 10px; padding:0 0 calc(10px + constant(safe-area-inset-bottom)); padding:0 0 calc(10px + env(safe-area-inset-bottom)); }

[BearJ]

@qingtiandalaoye 这里是针对iphone刘海屏的安全距离的写法