PX automatic conversion to REM error

Question

<style>html { font-size: calc(100vw / 3.75); }

body { font-size: 0.16rem; }</style>

< div class="box">hello php.cn</div>

/* The plug-in in the video is installed, and the automatically converted value of 200px is 12.5rem. It is calculated based on 16PX in the body. + izing: border- box; }</style>