Bootstrap navigation bar z-index issues are usually caused by improperly setting the cascaded context or position attribute. Common scenarios and solutions are as follows: 1. When the drop-down menu is blocked, set non-static positioning of the .dropdown parent and improve the z-index of .dropdown-menu to 1060; 2. When the fixed-top navigation bar is blocked, set the z-index of .navbar.fixed-top to 1030; 3. When multiple navigation elements interfere, unify the planning levels such as the main navigation 1030 and the floating toolbar 1040, and avoid abuse of z-index:9999. During troubleshooting, you should check whether the position attribute takes effect and use the developer tool to confirm the actual z-index value.

The z-index problem occurs in the navigation bar of Bootstrap, which is usually manifested as the drop-down menu is blocked by other elements, the fixed positioning of the navigation bar does not take effect, or some content is covered on the navbar. This problem is essentially not a bug in Bootstrap, but a problem with CSS cascading context.

Core reason: z-index only works in the same stacking context; if the position property is not set correctly, z-index is invalid.

Common Scene 1: The drop-down menu is blocked

If your .dropdown menu is obscured, especially in modal boxes, carousels, or other containers with overflow: hidden or transform set, it is mostly because these parent containers form a new cascade context.

Solution:

• Add a value other than position: static to the dropdown parent, such as relative .
• Improve the z-index of .dropdown-menu , such as adding a custom style:

 .dropdown-menu {
  z-index: 1060; /* a little higher than modal-backdrop*/
}

Note: If the navbar is in the modal, the z-index that comes with the modal is very high (usually 1050), you have to add it up.

Common Scenario 2: The fixed-top navigation bar is blocked

When using .fixed-top , the navigation bar will be separated from the document stream. At this time, if there are other targeting elements in the page (such as banner, ad, floating button, etc.), the navbar may be covered.

Solution:

• Check out the CSS of the occluded element to see if it has position: absolute/fixed/sticky and z-index .
• Set a reasonable z-index for .navbar.fixed-top , for example:

 .navbar.fixed-top {
  z-index: 1030;
}

The default level of Bootstrap is as follows:

• Navbar: 1030
• Dropdown: 1000
• Modal backdrop: 1040
• Modal: 1050

Common scenario three: multiple navbar or header elements interfere with each other

Sometimes the web page structure is relatively complex, such as main navigation and sub-navigation, or floating elements such as search bars and notification bars at the head, which may block each other due to the confusing level settings.

Suggested practices:

• Unified planning of the z-index level, such as:
  • Header Main Navigation: 1030
  • Top banner of page: 1020
  • Sub-navigation or floating toolbar: 1040
• Don't use z-index: 9999 casually, as it can easily cause difficulties in later maintenance.

Basically that's it.
In most cases, the problem can be solved by confirming whether the position attribute takes effect and setting z-index reasonably.
If it doesn't work, you can use the browser developer tool to check the computed style of the element to see what the z-index is in the actual application and whether its parent has truncated the cascade context.

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