Fixed at corner

<div style="
    position: relative;
">
    <!-- Top-left corner -->
    <div style="
        left: 0;
        position: absolute;
        top: 0;
    ">
        ...
    </div>

    <!-- Top-right corner -->
    <div style="
        position: absolute;
        top: 0;
        right: 0;
    ">
        ...
    </div>

    <!-- Bottom-right corner -->
    <div style="
        bottom: 0;
        position: absolute;
        right: 0;
    ">
        ...
    </div>

    <!-- Bottom-left corner -->
    <div style="
        bottom: 0;
        left: 0;
        position: absolute;
    ">
        ...
    </div>
</div>