.main {
height: 300px;
width: 300px;
display: flex;
flex-direction: column;
}
.item {
flex-grow: 1;
background-color: #0c0c0c;
}<div class="main"><div class="item"></div><div class="item"></div><div class="item"></div></div>
You can see white seams between divs.
The problem only happens in mobile phone view. Please copy into your text editor and open by chrome and press F12 to toggle to mobile phone view. Stackoverflow snippet doesn't recurrence the problem.