html , body{
    margin: 0;
    padding : 0;
}
body {
     /* 至少占满整个视口高度 */
    min-height: 100vh;
    background: #1b1f22;
    overflow: hidden;
}
body::before {
    content: "7";
    position: absolute;
    /* 根据高度计算 */
    font-size: calc(100vh / 1.5);
    /* 根据宽高比调整 */
    transform: scaleX(calc(100vw / 100vh));
    font-weight: bold;
    color: rgba(255,255,255,0.07);
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    z-index: 0;
}

.from_top{
    height : 12rem;
}

.header_line {
  width: 100%;
  max-width : 1000px;
  height: 1px;
  background-color: #ffffff;
}

.main{
    display: grid;
    place-items: center;
    height: 300px;
    
}
.main h1 {
    color: #ffffff;
    font-weight: 600;
    line-height: 1.5;
    margin: 0 0 1rem 0;
    font-size: 8rem;
    letter-spacing: 0.5rem;
}
.main p {
    color: #ffffff;
    font-size: 3rem;
}

nav ul {
    display: grid;
    grid-template-columns: repeat(4, 1fr); /* 4列等宽 */
    justify-content: center; /* 水平居中 */
    list-style: none;
    padding: 0;
    margin: 100px auto; /* 水平居中 */
    max-width: 1000px; /* 可选：限制最大宽度 */
    gap: 10px; /* 列间距 */
    border: solid 1px #ffffff;
    border-radius: 4px;
}
nav ul li {
    text-align : center;
    height: 2.75rem;
    border-left: solid 1px #ffffff;
}
nav ul li a {
    line-height: 2.75rem;
    letter-spacing: 0.2rem;
    font-size: 1.2rem;
    text-decoration: none;
    color : #ffffff;
}

@media (max-width: 768px) {
    .from_top {
        height: 0.5rem;
    }
    
    nav ul {
        margin : 0 auto;
        grid-template-columns: 1fr;
        max-width: 68rem;
    }
    
    nav ul li {
        border-left: none;
        border-bottom: 1px solid var(--border-color);
    }
    
    nav ul li:last-child {
        border-bottom: none;
    }
}

@media (max-width: 480px) {
    .main h1 {
        font-size: 3.5rem;
    }
    
    .main p {
        font-size: 1.1rem;
    }
    
    nav ul li a {
        padding: 0.8rem 0.5rem;
    }
}