nav {
    margin: 5px auto 0;
    position: relative;
    max-width: 1250px;
    height: 40px;
    padding: 5px;
    background-color: #fff;
    border: 0px solid #ddd;
    border-radius: 5px;
    display: flex;
    align-items: center;
    text-align: center;
    justify-content: center;
    font-size: 0;
    box-sizing: border-box; /* 追加 */
}

nav a {
    box-sizing: border-box; /* パディングを幅に含める */
    padding: 5px;
    line-height: 50px;
    height: 40px;
    font-size: 15px;
    display: inline-block;
    position: relative;
    z-index: 1;
    text-decoration: none;
    text-transform: uppercase;
    text-align: center;
    border-radius: 10px;
    color: #778899;
    cursor: pointer;
    /* 5個にそろえて20%ずつ */
    width: 20%;
}

/* アニメーション部分 */
nav .animation {
    position: absolute;
    height: 100%;
    top: 0;
    z-index: 0;
    transition: all .5s ease 0s;
    border-radius: 5px;
}

/* 5つに対応したアニメーション指定 */
nav .start-1,
nav a:nth-child(1):hover ~ .animation {
    width: 20%;
    left: 0;
    background-color: #ffc0cb;
}
nav .start-2,
nav a:nth-child(2):hover ~ .animation {
    width: 20%;
    left: 20%;
    background-color: #c3e8ff;
}
nav .start-3,
nav a:nth-child(3):hover ~ .animation {
    width: 20%;
    left: 40%;
    background-color: #eee8aa;
}
nav .start-4,
nav a:nth-child(4):hover ~ .animation {
    width: 20%;
    left: 60%;
    background-color: #c3ebc3;
}
nav .start-5,
nav a:nth-child(5):hover ~ .animation {
    width: 20%;
    left: 80%;
    background-color: #f7e9fd;
}

.footer {
    background-color: #ffffff;
    opacity: 0.85;
    position: fixed;
    bottom: 0vh;
    width: 100%;
}

.footer_navbar {
    background-color: #ffffff;
    padding: 0px;
    display: flex;
    align-items: center;
    bottom: 0;
    width: 100%;
    position: fixed;
    justify-content: space-between;
    z-index: 1000; /* フッターを前面に表示 */
}