project/assets/js/main/pages/404.vue

<template>
    <div class="page-404">
        <div class="flex-center position-ref full-height">
            <div class="code">404</div>
            <div class="message">Not Found</div>
        </div>
    </div>
</template>

<style lang="scss" scoped>
    .page-404 {
        background-color: #fff;
        color: #636b6f;
        font-weight: 400;
        height: 100vh;
        margin: 0;

        .full-height {
            height: 100vh;
        }

        .flex-center {
            align-items: center;
            display: flex;
            justify-content: center;
        }

        .position-ref {
            position: relative;
        }

        .code {
            border-right: 2px solid;
            font-size: 26px;
            padding: 0 15px 0 15px;
            text-align: center;
        }

        .message {
            font-size: 18px;
            padding: 10px;
            text-align: center;
        }
    }
</style>