Automatically Adjust the Size

Up until now you’ve been using pixels to set the size of things, e.g. 10px. On this card you will learn about other measurements you can use.

  • Go to index.html and find the img element with the picture of Tito, or find another img tag on your website.

  • Delete the width attribute if it’s there, and give the element an id if it doesn’t already have one.

<img src="tito.png" id="titoPicture" alt="Tito the dog" />
  • In your CSS file, define the width property for your picture as shown below (you might need to create the CSS block with the id selector if you haven’t already done so on a previous card).
#titoPicture {
  width: 50%;
  border-radius: 100%;
}

Note: 50% (50 percent) is half.

  • Try resizing your browser window and watch what happens to the picture.

You should see that the picture gets bigger and smaller when you make the window bigger and smaller. That is because it is taking up 50% of the width of the main element (which is roughly the width of the page).

How does it work?

When you set the size of something in pixels, you are setting an exact size and it doesn’t change. This is called an absolute measurement.

Another way to set the size of things is using relative measurements, so that size depends on how big elements are compared to each other. Then, whenever one thing changes size, everything else will automatically change size as well to keep the same proportions.

When you’re using relative measurements, it’s important to know what the parent of your element is. The parent is the thing that your element is inside of, and that’s what the measurement will be in relation to. For example, the parent of the image above is the article element, because the img element is in between the <article></article> tags.

If you set the width of an element to 100%, that will make it be the same width as the parent container it’s in.

  • Experiment with different numbers in front of the %.
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