Does commmeting affect the things outside?

Why this code shows border 7px

#content_area {
position: relative;
float: left;
background-color: #FFFFFF;
width: 100%;
border: 7px solid #FFFD33;
<!-- width: 125px; -->
}

but if I put border: 7px solid #FFFD33;after commeting:

#content_area {
position: relative;
float: left;
background-color: #FFFFFF;
width: 100%;
<!-- width: 125px; -->
border: 7px solid #FFFD33;
}

it doesn't ?

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