<div class="wrap">
  <p>左からauto：auto：autoの割合で自動で寸法割り当て</p>
  <div class="flex_container jcsb">
    <div class="flex_item flex_auto">auto</div>
    <div class="flex_item flex_auto">auto</div>
    <div class="flex_item flex_auto">auto</div>
  </div>
  <p>左からinitial：auto：auto</p>
  <div class="flex_container jcsb">
    <div class="flex_item flex_ini">ini</div>
    <div class="flex_item flex_auto">auto</div>
    <div class="flex_item flex_auto">auto</div>
  </div>
  <p>左からnone：initial：initial</p>
  <div class="flex_container jcsb">
    <div class="flex_item flex_none">none</div>
    <div class="flex_item flex_ini">ini</div>
    <div class="flex_item flex_ini">ini</div>
  </div>
  <p>左から１：２：５</p>
  <div class="flex_container jcsb">
    <div class="flex_item flex1">1</div>
    <div class="flex_item flex2">2</div>
    <div class="flex_item flex3">5</div>
  </div>
</div>
.flex_auto {
  flex: auto;
}
.flex_ini {
  flex: initial;
}
.flex_none {
  flex: none;
}
.flex1 {
  flex: 1;
}
.flex2 {
  flex: 2;
}
.flex3 {
  flex: 5;
}
.flex_container {
  width: 250px;
  border: 2px dotted black;
  display: flex;
}
.flex_item {
  width: 50px;
  height: 50px;
  border: 1px solid black;
  background-color: #008dab;
  display: flex;
  justify-content: center;
  align-items: center;
}

.wrap {
  min-width: max-content;
  margin: 0;
  padding: 10px;
  border: 1px solid gray;
  background-color: #ddd;
}
.wrap p {
  margin: 24px 0 5px;
}
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