Idea of Resize Vertical Icon
There is a single vertical arrow that has two arrow heads, each arrow head is pointing in an opposite direction with one of them going up and one of them going down.
This Resize Vertical icon is made in Material Design style
developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 6,100 icons, all in the same style and quality.