Why does using a percentage grid-gap in CSS Grid result in unexpected overflows?

Percentage Grid-Gap Overflow in CSS

In CSS Grid, setting the grid-gap property to a percentage value can lead to unexpected overflows. This issue arises because browsers handle percentage grid gaps differently.

Browser Behavior

Initially, the browser calculates the grid height, taking into account the content within the grid cells. However, it ignores the percentage grid gap (treating it as auto). This calculation results in a tight spacing between grid cells.

Calculating Height

To calculate the grid height, the browser evaluates the height of each grid cell and adds the content's margins and paddings, but not the grid gap:

console.log(document.querySelector('.grid').offsetHeight);

Resolving the Issue

To avoid overflows, consider the following approaches:

• Use Fixed Values: Replace percentage grid gaps with fixed values (e.g., pixels or ems) to ensure consistent spacing.
• Define Grid Template Rows/Columns: This allows you to explicitly specify row/column heights and remove the dependency on content height.
• Use Flexible Track Sizes: Consider using flexible track sizes (e.g., fr) to distribute the available space more evenly among grid cells.

Additional Note

Opacity does not affect grid cell height calculations. If you need to hide or display grid items dynamically, use a different approach such as display: none.

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