Append a line below "window" in app.json
"navigationStyle": "custom"
The white background bar at the top of the mini program disappeared and became transparent, leaving only the capsule button in the upper right corner.
warn:
If the page has
<web-view src="{
{src}}" />
For this element, the background color of the top title bar will still appear~~
Extended reading : How to hide the navigationBar at the top of the H5 page of the uniapp development applet? Three Solutions_Uniapp Top Status Bar_Your Beloved Brother Qiang’s Blog-CSDN Blog [Code] How to hide the navigationBar at the top of the H5 page of the uniapp development applet? _uniapp top status bar 
https://szq.blog.csdn.net/article/details/131226906