Align two divs horizontally

html css

.container {
display: flex;
}

<div class="container">
<div>
<span>source list</span>
<select size="10">
<option />
<option />
<option />
</select>
</div>

<div>
<span>destination list</span>
<select size="10">
<option />
<option />
<option />
</select>
</div>
</div>

Reference

https://stackoverflow.com/questions/2417130/how-can-i-align-two-divs-horizontally