Add vertical scroll bar to panel

I am trying to make a Panel scrollable, but only vertically (so AutoScroll won't work because the child controls go past the left edge and must).

So how is this done?

Try this instead for 'only' scrolling vertical.
(auto scroll needs to be false before it will accept changes)

mypanel.AutoScroll = false;
mypanel.HorizontalScroll.Enabled = false;
mypanel.HorizontalScroll.Visible = false;
mypanel.HorizontalScroll.Maximum = 0;
mypanel.AutoScroll = true;

Assuming you're using winforms, default panel components does not offer you a way to disable the horizontal scrolling components. A workaround of this is to disable the auto scrolling and add a scrollbar yourself:

ScrollBar vScrollBar1 = new VScrollBar();
vScrollBar1.Dock = DockStyle.Right;
vScrollBar1.Scroll += (sender, e) => { panel1.VerticalScroll.Value = vScrollBar1.Value; };
panel1.Controls.Add(vScrollBar1);

Detailed discussion here.

Panel has an AutoScroll property. Just set that property to True and the panel will automatically add a scroll bar when needed.

AutoScroll is really the solution! You just have to set AutoScrollMargin to 0, 1000 or something like this, then use it to scroll down and add buttons and items there!

Below is the code that implements custom vertical scrollbar. The important detail here is to know when scrollbar is needed by calculating how much space is consumed by the controls that you add to the panel.

panelUserInput.SuspendLayout();
panelUserInput.Controls.Clear();
panelUserInput.AutoScroll = false;
panelUserInput.VerticalScroll.Visible = false;

// here you'd be adding controls

int x = 20, y = 20, height = 0;
for (int inx = 0; inx < numControls; inx++ )
{
    // this example uses textbox control
    TextBox txt = new TextBox();
    txt.Location = new System.Drawing.Point(x, y);
    // add whatever details you need for this control
    // before adding it to the panel
    panelUserInput.Controls.Add(txt);
    height = y + txt.Height;
    y += 25;
}
if (height > panelUserInput.Height)
{
    VScrollBar bar = new VScrollBar();
    bar.Dock = DockStyle.Right;
    bar.Scroll += (sender, e) => { panelUserInput.VerticalScroll.Value =  bar.Value; };
    bar.Top = 0;
    bar.Left = panelUserInput.Width - bar.Width;
    bar.Height = panelUserInput.Height;
    bar.Visible = true;
    panelUserInput.Controls.Add(bar);
}
panelUserInput.ResumeLayout();

// then update the form
this.PerformLayout();

Add to your panel's style code something like this:

<asp:Panel ID="myPanel" runat="Server" CssClass="myPanelCSS" style="overflow-y:auto; overflow-x:hidden"></asp:Panel>