How to realize that the width of the navigation bar is the same as that of the browser

as shown in the picture, I set the width to 100% in the future, but there is always a scroll bar below the browser that does not match the width of the browser

Mar.02,2021

you have to post the code to analyze
guess that you didn't do reset
* {
margin:0;
padding:0
}
html,body {
width:100%
}

.
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