This article aims to solve the problem of inaccurate positioning of drop-down menus in the navigation bar, especially when position: absolute cannot be responsively adjusted, and position: relative in turn causes the menu to disappear. The core solution is to correctly manage the overflow properties of the parent element and set position: relative for the drop-down menu container to create a positioning context, while optimizing the mobile display through media queries to ensure that the drop-down menu can be positioned accurately and responsively under its trigger button at any screen size.

Understand the challenges of drop-down menu positioning

When building a navigation bar with a drop-down menu, developers often encounter a tricky problem: how to make sure the drop-down menu is always positioned precisely under its trigger button and maintains good performance at different screen sizes. A common problem is that when using position: absolute, the drop-down menu may be fixed at a certain position in the viewport and does not move with the parent element or browser window resize; and when trying to use position: relative, the drop-down menu may disappear completely. This is usually due to insufficient understanding of the CSS box model, positioning properties and its interaction with the overflow properties.

The influence of core positioning principle and overflow attributes

To achieve accurate and responsive drop-down menu positioning, we need to master the following key CSS concepts:

1. position: relative : When an element is set to position: relative, it is positioned relative to its normal position. More importantly, it provides a positioning context for any descendant position: absolute element. This means that if a child element is set to position: absolute, its position (such as top, left, right, bottom) will be calculated relative to the most recent position: relative (or absolute, fixed, sticky) ancestor element, rather than relative to the viewport.
2. position: absolute : The element is separated from the document stream and positioned relative to its nearest positioned ancestor element. If there is no positioned ancestor element, it will be positioned relative to the initial containing block (usually the element).
3. overflow: hidden : This property trims the element's contents so that it does not exceed the element's inner margin box. If a parent element has overflow: hidden and its child elements (especially the child element of position: absolute) exceed the boundary of the parent element, the excess will be hidden. This is the culprit that causes the drop-down menu to "disappear" in some cases.

Solution: Build a responsive drop-down menu

In order to solve the positioning problem of the drop-down menu, we need to make the following key adjustments to the original code:

1. Remove unnecessary overflow: hidden

In the original code, both .navbar and .dropdownL have overflow: hidden. This causes the dropdown menu (.dropdown-contentL) to be clipped when rendering outside these parent elements. In order to allow the drop-down menu to be displayed freely, we need to remove these restrictions.

CSS tuning example:

 .navbar {
  /* overflow: hidden; */ /* Remove this line*/
  background-color: #333;
  font-family: Arial, Helvetica, sans-serif;
  /* Other styles remain unchanged*/
}

.dropdownL {
  float: left;
  /* overflow: hidden; */ /* Remove this line*/
  position: relative; /* Add or modify*/
}

2. Set the positioning context for the drop-down menu container

Setting .dropdownL (including buttons and dropdown content) to position: relative can provide a positioning context for its child element .dropdown-contentL (the dropdown menu itself). In this way, the position: absolute of .dropdown-contentL can be positioned relative to .dropdownL.

CSS tuning example:

 .dropdownL {
  float: left;
  /* overflow: hidden; */ /* Removed*/
  position: relative; /* Make sure this property exists*/
}

3. Keep the absolute positioning of the drop-down menu content

.dropdown-contentL keeps position: absolute and set left: 0 to align its left edge with the left edge of the parent .dropdownL. Since .dropdownL is now position: relative, the dropdown menu will be positioned precisely below its trigger button.

CSS tuning example:

 .dropdown-contentL {
  display: none;
  position: absolute;
  background-color: #f9f9f9;
  width: 400px;
  left: 0; /* Keep this property*/
  box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
  z-index: 1;
}

4. Enhanced responsive design: mobile terminal center display

To provide a better user experience on small screen devices, we can use media queries to adjust the positioning of the drop-down menu. For example, when the screen width is less than or equal to 768px, let the drop-down menu center in the horizontal direction.

CSS tuning example:

 @media screen and (max-width: 768px) {
  .dropdownL {
    position: unset; /* or position: static; Allow it to restore to normal document flow*/
  }

  .dropdown-contentL {
    left: 0;
    right: 0;
    margin-left: auto;
    margin-right: auto;
    width: 90%; /* Optional: Adjust width to fit small screen*/
  }
}

In the above media query:

• position: unset is applied to .dropdownL, making it no longer a positioning context under a small screen, allowing its content (including the drop-down menu) to be more flexible.
• left: 0; right: 0; margin-left: auto; margin-right: auto; combined with position: absolute, the element can be centered horizontally in the available space.

Complete code example

The following is modified and optimized HTML and CSS code that demonstrates how to implement a responsive and accurate positioning drop-down menu.

HTML (stay unchanged, but again for completeness):

 


    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Responsive drop-down menu</title>
    <link rel="stylesheet" type="text/css" href="./index.css">
    <!-- Introduce Font Awesome icon library, if needed -->
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">


    <div class="navigationrow">
        <div class="navbar">
            <div><a href="#home">One</a></div>
            <div><a href="#news">Two</a></div>
            <div class="dropdownL">
                <button class="dropbtnL">
                    Three
                    <i class="fa fa-caret-down"></i>
                </button>
                <div class="dropdown-contentL">
                    <div class="header">
                        <h2>Menu</h2>
                    </div>
                    <div class="row">
                        <div class="column">
                            <h3>Category 1</h3>
                            <a href="#">Link 1</a>
                            <a href="#">Link 2</a>
                            <a href="#">Link 3</a>
                        </div>
                        <div class="column">
                            <h3>Category 2</h3>
                            <a href="#">Link 1</a>
                            <a href="#">Link 2</a>
                            <a href="#">Link 3</a>
                        </div>
                        <div class="column">
                            <h3>Category 3</h3>
                            <a href="#">Link 1</a>
                            <a href="#">Link 2</a>
                            <a href="#">Link 3</a>
                        </div>
                    </div>
                </div>
            </div>
        </div>
    </div>

CSS (index.css):

 * {
    box-sizing: border-box;
}

body {
    margin: 0;
}

.navbar {
    /* Remove overflow: hidden; */
    background-color: #333;
    font-family: Arial, Helvetica, sans-serif;
    display: grid; /* Keep grid layout*/
    grid-template-columns: repeat(4, 1fr); /* Adjust to more flexible 1fr */
    grid-template-rows: 46px;
    border: white 1px solid;
}

.navbar a {
    /* float: left; */ /* float is no longer necessary under grid layout*/
    font-size: 16px;
    color: white;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    display: flex; /* Use flex to center content*/
    align-items: center;
    justify-content: center;
}

.dropdownL {
    /* float: left; */ /* float is no longer necessary under grid layout*/
    /* Remove overflow: hidden; */
    position: relative; /* Key: Provide positioning context for the drop-down menu*/
    display: flex; /* Use flex center button*/
    align-items: center;
    justify-content: center;
}

.dropdownL .dropbtnL {
    font-size: 16px;
    border: none;
    outline: none;
    color: white;
    padding: 14px 16px;
    background-color: inherit;
    font: inherit;
    margin: 0;
    cursor: pointer; /* Add mouse pointer style*/
}

.navbar a:hover,
.dropdownL:hover .dropbtnL {
    background-color: red;
}

.dropdown-contentL {
    display: none;
    position: absolute;
    background-color: #F9F9F9;
    width: 400px;
    left: 0; /* Position relative to the left edge of .dropdownL*/
    box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
    z-index: 1;
    top: 100%; /* Make sure the drop-down menu appears below the button*/
}

.dropdown-contentL .header {
    background: red;
    padding: 16px;
    color: white;
}

.dropdownL:hover .dropdown-contentL {
    display: block;
}

/* Create three equal columns that floats next to each other */
.row {
    display: flex; /* Use flexbox instead of float */
}

.column {
    /* float: left; */ /* Remove float */
    flex: 1; /* Make column equal width*/
    width: 33.33%; /* Keep the original width, but flex: 1 is more powerful*/
    padding: 10px;
    background-color: #CCC;
    height: 250px;
}

.column a {
    /* float: none; */ /* Remove float */
    color: black;
    padding: 16px;
    text-decoration: none;
    display: block;
    text-align: left;
}

.column a:hover {
    background-color: #DDD;
}

/* Clear floats after the columns */
/* .row::after { /* No longer required under flexbox layout*/
/* content: "";
    display: table;
    clear: both;
} */


/* Responsive adjustment*/
@media screen and (max-width: 768px) {
    .navbar {
        grid-template-columns: 1fr; /* vertical stacking of navigation items under small screen*/
        grid-template-rows: auto;
    }
    .navbar > div {
        width: 100%;
    }

    .dropdownL {
        position: unset; /* Remove the positioning context and allow it to position normally in the document stream*/
        width: 100%;
    }

    .dropdown-contentL {
        position: absolute; /* is still absolute positioning, but now relative to the viewport or the nearest positioned ancestor*/
        left: 0;
        right: 0;
        margin-left: auto;
        margin-right: auto;
        width: 90%; /* Adjust width to fit small screen*/
        max-width: 400px; /* limit maximum width*/
        top: auto; /* Reset top property*/
    }
    .row {
        flex-direction: column; /* columns are stacked vertically*/
    }
    .column {
        width: 100%;
        height: auto; /* Highly adaptable*/
    }
}

Notes and best practices:

• top: 100% : To ensure that the drop-down menu is always below the button, it is recommended to explicitly set top: 100% in .dropdown-contentL. This aligns the top edge of the dropdown menu with the bottom edge of the parent .dropdownL.
• Grid and Flexbox compatibility : In the original code, .navbar uses display: grid, while the child elements use float. In modern CSS, it is generally recommended to avoid floats in grids or elastic layouts, as they can lead to inconsistent behavior. The above example has tried replacing float with flex related properties to better work with grid layout.
• Semantic HTML : Make sure your HTML structure is semantic, for example wrapping the navigation bar with the
• Accessibility : For the drop-down menu, in addition to visual effects, keyboard navigation and screen reader support also need to be considered. For example, use ARIA attributes (aria-haspopup, aria-expanded) and appropriate JavaScript to manage focus.
• Animation effect : You can add smooth animation effects to the display/hide of the drop-down menu through the CSS transition attribute to improve the user experience.

Summarize

To solve the problem of positioning on the navigation bar drop-down menu, the key is to understand the collaborative working mechanism of CSS positioning attributes (position: relative and position: absolute), and the impact of the overflow attribute on absolute positioning child elements. By setting position: relative for the drop-down menu container to create a positioning context and removing unnecessary overflow: hidden, you can ensure that the drop-down menu is positioned precisely below the trigger button. At the same time, a responsive layout is achieved in combination with media queries, which can provide users of different devices with a consistent and friendly interactive experience. Following these principles, you can build a robust and easy-to-maintain pull-down menu component.

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