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In Bootstrap 3 all columns have a padding on the sides of 15px for each side.
.col-lg-1, .col-lg-10, .col-lg-11, .col-lg-12, .col-lg-2, .col-lg-3, .col-lg-4, .col-lg-5, .col-lg-6, .col-lg-7, .col-lg-8, .col-lg-9, .col-md-1, .col-md-10, .col-md-11, .col-md-12, .col-md-2, .col-md-3, .col-md-4, .col-md-5, .col-md-6, .col-md-7, .col-md-8, .col-md-9, .col-sm-1, .col-sm-10, .col-sm-11, .col-sm-12, .col-sm-2, .col-sm-3, .col-sm-4, .col-sm-5, .col-sm-6, .col-sm-7, .col-sm-8, .col-sm-9, .col-xs-1, .col-xs-10, .col-xs-11, .col-xs-12, .col-xs-2, .col-xs-3, .col-xs-4, .col-xs-5, .col-xs-6, .col-xs-7, .col-xs-8, .col-xs-9 {
position: relative;
min-height: 1px;
padding-right: 15px;
padding-left: 15px;
}
Just change this value in paddings to "narrow" that gap between one column and another.
Here is the official documentation and you can check the default value of the standard "Gutter" https://getbootstrap.com/docs/3.3/css/#grid-options
Example with padding adjusted, decreases from standard 15px on each side to 6px on each side
div[class^="col-"] {
box-sizing: border-box;
border: 1px solid red;
padding-left: 6px !important;
padding-right: 6px !important;
}
.bg {
width: 100%;
height: 50px;
background-color: aquamarine;
}
<link rel="stylesheet" type="text/css" media="screen" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" />
<div class="container">
<div class="row">
<div class="col-xs-4"><div class="bg">1</div></div>
<div class="col-xs-4"><div class="bg">2</div></div>
<div class="col-xs-4"><div class="bg">3</div></div>
</div>
</div>


Which version of Bootstrap?
– hugocsl
@hugocsl version 3
– Lia