Fixed at corner

<div class="fixed-at-corner">
    <!-- Top-left corner -->
    <div class="fixed-at-corner__corner fixed-at-corner__corner--tl">...</div>

    <!-- Top-right corner -->
    <div class="fixed-at-corner__corner fixed-at-corner__corner--tr">...</div>

    <!-- Bottom-right corner -->
    <div class="fixed-at-corner__corner fixed-at-corner__corner--br">...</div>

    <!-- Bottom-left corner -->
    <div class="fixed-at-corner__corner fixed-at-corner__corner--bl">...</div>
</div>

.fixed-at-corner {
    position: relative;
}

.fixed-at-corner__corner {
    position: absolute;
}

.fixed-at-corner__corner--tl {
    left: 0;
    top: 0;
}

.fixed-at-corner__corner--tr {
    top: 0;
    right: 0;
}

.fixed-at-corner__corner--br {
    bottom: 0;
    right: 0;
}

.fixed-at-corner__corner--bl {
    bottom: 0;
    left: 0;
}