Achieving Percentage Width/Height minus Pixels in CSS

However, there are workarounds to achieve a similar effect. Here are two common approaches:

1. Negative Margins:

   • Apply a positive width/height percentage to the element (e.g., width: 80%).
   • Add a negative margin on the left and right (or top and bottom) sides of the element equal to the pixel value you want to subtract (e.g., margin-left: -50px; margin-right: -50px;).
   • Make sure the parent container of the element has overflow: hidden; set. This ensures the element doesn't overflow the available space due to the negative margins.

2. Calc Function (Less Common):

   • While not directly supported in all browsers, the calc function can be used in some scenarios. It allows basic mathematical operations within CSS properties. However, browser compatibility might be an issue.
   • Example: width: calc(100% - 50px); (check browser compatibility before using).

Here are some things to keep in mind:

• The negative margin approach is more widely supported and generally recommended.
• Using the calc function might require checking for browser compatibility.
• Consider using a CSS preprocessor like Sass or Less, which can compile the calc function for broader browser support.

<div class="container">
  <div class="content">This content will have 80% width minus 50px on each side.</div>
</div>

.container {
  overflow: hidden; /* Ensures content doesn't overflow */
}

.content {
  width: 80%;
  margin-left: -50px;
  margin-right: -50px;
  /* Add other styles like padding or background color here */
}

Calc Function (Less Common - Check Browser Compatibility):

<div class="content">This content will have calculated width (100% minus 50px).</div>

.content {
  width: calc(100% - 50px);
  /* Add other styles like padding or background color here */
}

Flexbox with flex-grow (Limited Use Case):

This method works well if you have a container element with child elements that should take up the remaining space after accounting for a specific pixel value.

Here's how it works:

<div class="container">
  <div class="fixed-width">This element will have a fixed width (e.g., 100px).</div>
  <div class="flexible-content">This element will fill remaining space.</div>
</div>

.container {
  display: flex; /* Enable flexbox */
}

.fixed-width {
  width: 100px; /* Set your desired fixed width */
}

.flexible-content {
  flex: 1; /* Allow this element to grow and fill remaining space */
}

Note: This method won't work if you need the element to have a specific percentage of the remaining space. It's more suitable for situations where the flexible content should simply fill the leftover space.

CSS Grid with fr units (Modern Browsers):

Similar to flexbox, CSS Grid with fr units allows you to define the size of grid tracks based on fractions of the available space.

Here's an example:

<div class="container">
  <div class="fixed-width">This element will have a fixed width (e.g., 100px).</div>
  <div class="flexible-content">This element will fill remaining space.</div>
</div>

.container {
  display: grid;
  grid-template-columns: 100px 1fr; /* Define grid tracks: fixed width, then 1 fraction unit */
}

.fixed-width {
  /* No additional styles needed here */
}

.flexible-content {
  /* Add other styles like padding or background color here */
}