How to stretch the background image to fill a div

Controlling the image aspect ratio: Aspect ratio matters

Sometimes, maintaining the image's original aspect ratio is a win—background-size: cover; is your best friend in such cases! Although, keep in mind that some parts of your image may be truncated on certain devices:

div {
  background-image: url('cool-image.jpg');
  background-size: cover; /* Keeps the original proportions like a skilled tailor */
}
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But on some days, you need an image adjustment that's complete without cropping or distortion. Say "Hello!" to background-size: contain;. This property scales the image to its best fit within the div, beautifully showcasing the entire image but could possibly create some extra space.

Dealing with old browsers: Time machines don't exist

Not all browsers have moved with the times. Here's a candy for the old browsers that don't support the background-size property. A simple CSS hack utilizing absolute positioning with width and height set to 100% can closely mimic background-size:

#parent-div {
  position: relative;
}

#old-browser-img {
  /* Because old browsers need love too */
  position: absolute; 
  width: 100%;
  height: 100%;
}
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JavaScript to the rescue: When CSS is not enough

In spaces where CSS falls short, JavaScript steps in like a superhero. By using utilities like jQuery, dynamically centering and adjusting images to mimic properties like background-size: cover or contain becomes a walk in the park:

function resizeBackground() {
  var $div = $('#your-div');
  var $img = $('#your-div img');

  // Calculate aspect ratio like Pythagoras would and adjust accordingly
  var aspectRatio = $img.width() / $img.height();
  if (window.innerWidth / window.innerHeight < aspectRatio) {
    $img.css('height', '100%');
    $img.css('width', 'auto');
  } else {
    $img.css('width', '100%');
    $img.css('height', 'auto');
  }
}

$(window).on('resize', resizeBackground);
resizeBackground(); // Initiate Operation Resize
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Posing with advanced techniques and best practices

Responsive design considerations: One size does not fit all

A responsive design adapts to different body shapes—I mean, screen sizes. In such scenarios, media queries can tweak the background-size accordingly, and you can combine cover with background-position and percentages to keep your image looking its best:

@media (max-width: 768px) {
  div {
    background-size: 100% 100%; 
    /* Smartphone users will thank you */
  }
}

@media (min-width: 769px) {
  div {
    background-size: cover; 
    /* Grand panorama for larger screens */
  }
}
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Performance implications: Speed is key

Working with large images? Attend the performance by using optimized images to reduce load times, combine this with the no-repeat rule and smart positioning to achieve professional design:

div {
  background-image: url('optimized-image.jpg'); /* Tune up your image */
  background-repeat: no-repeat; /* Smooth design, smooth life */
  background-position: top left; /* Aligns with the stars */
}
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Using CSS3 for a modern twist

Modern times call for modern measures:

• background-attachment: fixed; delivers the much-coveted parallax effect
• background-clip and background-origin serve up a rich design sauce

div {
  /* Cosmopolitan design incoming */
  background-size: contain;
  background-attachment: fixed;
}
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