trying to make canvas fill page under a title

i want the canvas to fill the whole webpage under the heading, maybe with a small margin between the edge of the canvas and the edge of the window. but i can't get it to fill the screen and now the title is next to it instead of above it. any help is appreciated

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>shark?</title>
    <style>
        html, body {
            height: 100%;
            width: 100%;
            margin: 0;
        }
        .container {
            display: flex;
            align-items: center;
            justify-content: center;
            height: 100%;
            width: 100%;
        }
        canvas {
            background-color: dodgerblue;
        }
    </style>
</head>
<body>
    <div class="container">
        <h1>shark?</h1>
        <canvas></canvas>
    </div>
</body>
</html>

Solution

Adding the property flex-direction: column; to the container class to arrange the elements vertically.

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>shark?</title>
    <style>
        html, body {
            height: 100%;
            width: 100%;
            margin: 0;
            overflow: hidden; /* Prevent scrollbars */
        }
        .container {
            display: flex;
            flex-direction: column; /* Arrange elements vertically */
            align-items: center;
            justify-content: center;
            height: 100%;
            width: 100%;
        }
        h1 {
            margin-top: 20px; /* Add margin above the heading */
        }
        canvas {
            background-color: dodgerblue;
            margin: 10px; /* Add margin around the canvas */
            flex: 1; /* Allow the canvas to fill available vertical space */
            width: calc(100% - 20px); /* Account for margin */
        }
    </style>
</head>
<body>
    <div class="container">
        <h1>shark?</h1>
        <canvas></canvas>
    </div>
</body>
</html>