Fluid images refer to images that can resize and adapt to different screen sizes and devices. However, sometimes when using fluid images within a div container, a common issue called "div slightly out" may occur. In this article, we will explore the reasons behind this issue and provide a solution.

The reason why the "div slightly out" issue occurs is due to the default behavior of the line-height property. When an image is placed within a div container, the default line-height value causes a small space to appear at the bottom of the container, making the image slightly pushed out.

To solve this issue, we can set the line-height property to 0 for the div container. This can be achieved by using the following CSS code:

line-height: 0;

Setting the line-height to 0 is essentially equivalent to setting the font-size to 0 pixels. This eliminates the space caused by the default line-height value and prevents the image from being pushed out of the div container.

By applying this solution, we can ensure that fluid images within a div container are displayed without any unwanted gaps or misalignment. This is particularly important when designing responsive websites that need to adapt to various screen sizes and devices.

In conclusion, the "div slightly out" issue can be resolved by setting the line-height property to 0 for the div container. This simple solution ensures that fluid images within the container are displayed correctly and without any spacing issues. By understanding the cause of this issue and applying the appropriate solution, web developers can create seamless and visually appealing designs for their websites.

问题出现的原因是图片元素的默认display属性为inline-block，但是这样设置无效。解决方法是将图片元素的display属性设置为block或者inline-block。根据HTML5的描述，这样做可以解决这个问题。另外，虽然图片元素的display属性默认是inline，但是它更精确地被称为"replaced inline element"。虽然设置为inline-block有一些效果，但它并不完全相同。因此，将display属性设置为block是一个好的解决方法，而将其设置为inline-block则无效。

这个问题的出现是由于图像的行为类似于文本中的一个字符（因此会在图像下方留下一个空白，就像"y"或"g"的下悬部分一样），并且通过使用vertical-align CSS属性来指示不需要这样的空间来解决这个问题。几乎任何vertical-align的值都可以；我个人喜欢middle。

问题是由于vertical-align: baseline引起的，这是大多数元素的默认值，表示应该保留该空间。一些其他合法的vertical-align值也会保留这个空间，但top、text-top、middle、bottom和text-bottom不会保留。虽然sub也不会保留，但我不太相信它。

如果图像比字体大小小，则这种方法不起作用，因为即使不保留那个“特殊”空间，div仍然会保留足够的空间来放置文本。在这种情况下，您将不得不使用pantryfight的建议或display: block来完全移除图像中的文本。

这也适用于iframe（例如嵌入的YouTube视频或Google地图）。

2021年了，这仍然是最好的答案！