how to reduce the gap between 2 flex items code example

Example 1: css flex gap between items

/* limited support (Q1/2021: Firefox, Chrome, Safari) */
.flex-container
{
  display: flex;
  gap: 5px;
}

/* broad support */
.flex-item
{
  margin: 5px;
  /* and/or */
  padding: 5px;
}

Example 2: gap between two flex items

.upper
{
  margin:30px;
  display:flex;
  flex-direction:row;
  width:300px;
  height:80px;
  border:1px red solid;

  padding:5px; /* this */
}

.upper > div
{
  flex:1 1 auto;
  border:1px red solid;
  text-align:center;

  margin:5px;  /* and that, will result in a 10px gap */
}

.upper.mc /* multicol test */
{flex-direction:column;flex-wrap:wrap;width:200px;height:200px;}