CSS導航欄特效可以讓網站菜單更加美觀、易用、互動性更強。下面是一些常見的CSS導航欄特效，以供參考。

/* 1. 懸停下劃線特效 */
a {
position: relative;
text-decoration: none;
}
a::after {
content: '';
position: absolute;
left: 0;
bottom: -2px;
width: 100%;
height: 2px;
background-color: #000;
transform: scaleX(0);
transition: transform 0.3s ease;
}
a:hover::after {
transform: scaleX(1);
}
/* 2. 懸停背景色特效 */
a {
padding: 10px;
background-color: #fff;
transition: background-color 0.3s ease;
}
a:hover {
background-color: #000;
color: #fff;
}
/* 3. 點擊下拉菜單特效 */
.dropdown {
position: relative;
display: inline-block;
}
.dropdown-content {
display: none;
position: absolute;
z-index: 1;
}
.dropdown:hover .dropdown-content {
display: block;
}
/* 4. 按鈕反轉顏色特效 */
.btn {
padding: 10px 20px;
border: 2px solid #000;
color: #000;
transition: background-color 0.3s ease, color 0.3s ease;
}
.btn:hover {
background-color: #000;
color: #fff;
}
/* 5. 下拉列表特效 */
.select {
display: inline-block;
position: relative;
}
.select select {
padding: 10px;
background-color: #fff;
border: none;
appearance: none;
-webkit-appearance: none;
-moz-appearance: none;
cursor: pointer;
}
.select::after {
content: '\25BC';
position: absolute;
right: 10px;
top: 50%;
transform: translateY(-50%);
pointer-events: none;
}

以上CSS導航欄特效可以根據需求進行自由組合和拓展，如果想要更多更酷炫的CSS導航欄特效，可以繼續學習CSS animation、transform、transition等技術。