Complete Server Lockdown

Hey there, I am trying to make a command which locks the whole server in discord.py but when I use the command, it just locks the channel which I used it in. Please help me if you can, Here is my current code.

@client.command()
@commands.has_permissions(manage_channels=True)
async def lockdown(ctx):
    await ctx.channel.set_permissions(ctx.guild.default_role,send_messages=False)
    embedVar3 = discord.Embed(
      title="Locked",
      description=(f'***Server has been locked.***'),
    colour=(0x0000ff))
    await ctx.send(embed=embedVar3)