fix(navbar): fix styles when navbar is not present

[Aterbonus]

Before

After

[ulivz]

Can you provide more context? I cannot repro this bug.

[Aterbonus]

When a page has no navbar (navbar: false in the front matter) there is a gap where the navbar was.

This is especially evident when we use a Custom Layout and we don't want to have a navbar.

Example:

HomeLayout.vue

<template>
<div class="container">
    <vue-nixie-clock></vue-nixie-clock>
</div>
</template>

<style scoped>
.container {
    align-items: center;
    background-color: #000;
    display: flex;
    height: 100vh;
    justify-content: center;
}

.nixie-clock {
    width: 800px;
}
</style>

README.md

---
layout: HomeLayout
navbar: false
---

Before

After

[meteorlxy]

Why not add some mark on the snapshots? I even can't find the differences at first...

[ulivz]

Checked at my local and LGTM, only a small question.

[ulivz]

Why need reset top: 0 here ?

[Aterbonus]

When there is no navbar, setting top to 0 will cause the sidebar to have 100% height of the viewport on Desktop.

Before

After

[ulivz]

Thanks for the work!