Simple Deposit Account (Don't Use - Intro Version for Safety Discussion)

deposit-account.sol

pragma solidity >=0.4.22 <0.6.0;
contract DepositAccount {
    address payable owner;

    constructor() public {
        owner = msg.sender;
    }
    
    function withdraw() public {
        require(owner == msg.sender);

        owner.transfer(address(this).balance);
    }
    
    function withdraw(uint256 amount) public {
        require(owner == msg.sender);
        require(address(this).balance >= amount);
        
        owner.transfer(amount);
    }
    
    function() payable external {}
}