CSS:

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button {
  border-radius: 50%; /* makes the button round */
  width: 50px; /* adjust the width according to your preference */
  height: 50px; /* adjust the height according to your preference */
  margin: 0 auto; /* centers the button */
  transition: all 200ms ease-in-out; /* creates a smooth transition for all button changes */
}

Note:

• You can adjust the border-radius, width, and height values to match your design requirements.
• The transition property applies a smooth transition to all button changes, including when you hover over the button.

HTML:

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<button class="round-button"></button>

CSS:

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.round-button {
  border-radius: 50%;
  width: 50px;
  height: 50px;
}

This will create a round button with a diameter of 50 pixels. You can adjust the width and height property to fit your needs.

I assume you are referring to how to add a box using HTML and CSS.

You can add a box in HTML by using the <div> tag, which creates a container for other HTML elements. Then, use CSS to style the box by applying different properties such as width, height, border, padding, margin, and more.

Here's an example:

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<div class="box">
  This is a box!
</div>

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.box {
  width: 200px;
  height: 100px;
  border: 1px solid black;
  padding: 10px;
  margin: 10px;
}

In this example, we created a box with class name box, set its width and height to 200px and 100px respectively, added a 1px solid black border, 10px of padding, and 10px of margin around the box.

You can adjust these values to create a box that fits your requirements.

To make an image fit the browser window while changing, you can use CSS to set the image's maximum width to 100% and height to auto. This will ensure that the image resizes dynamically as the browser window size changes. Here's an example in CSS:

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img {
  max-width: 100%;
  height: auto;
}

You can add this CSS to an external stylesheet or include it in a <style> tag in the head of your HTML document.

Here's an example of how you could create a simple smiley face using HTML and CSS:

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<!-- HTML Code -->
<div class="smiley-face">
  <div class="eyes"></div>
  <div class="mouth"></div>
</div>

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/* CSS Code */
.smiley-face {
  width: 100px;
  height: 100px;
  border-radius: 50%;
  background-color: yellow;
  position: relative;
}

.eyes {
  position: absolute;
  top: 25%;
  left: 20%;
  width: 15%;
  height: 15%;
  border-radius: 50%;
  background-color: black;
}

.eyes + .eyes {
  left: 65%;
}

.mouth {
  position: absolute;
  top: 50%;
  left: 20%;
  width: 60%;
  height: 20%;
  border-radius: 50%;
  border-top: 3px solid black;
}

The code above creates a div element with the class smiley-face. This div element has two child elements, which are also div elements: one for the eyes and one for the mouth. The styling for each element is done using CSS.

The smiley-face div has a width and height of 100 pixels, and its border-radius is set to 50% to make it circular. The background color is set to yellow to represent the face's color.

The eyes are created as two div elements with a black background color and border-radius set to 50% to make them circular. They are positioned using the position property and top and left values.

The mouth is created as a div element with a border radius of 50% and a top border of 3 pixels thick to represent a smile. It is positioned in the center of the face using the top and left properties.

By applying the CSS code, the result will be a cute little smiley face with black eyes and smiling mouth.

To add an image to an HTML page, you can use the img tag. Here's an example:

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<img src="image-url.jpg" alt="description of image">

In the src attribute, you should provide the URL of the image you want to display on your page. The alt attribute should provide a text description of the image, which is helpful for those who may not be able to see the image due to accessibility issues. Make sure to replace image-url.jpg with the actual URL of your image.

You can also provide optional attributes to control the size and alignment of the image. Here's an example:

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<img src="image-url.jpg" alt="description of image" width="500" height="200" align="center">

In the example above, the width and height attributes control the size of the image, while the align attribute centers it within its parent element.

To set the size of an image in CSS, you can use the width and height properties. You can set the value of these properties to the desired width and height of the image in pixels or percentages. Here's an example code block using CSS:

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img {
  width: 200px;
  height: 150px;
}

In this example, the width property of the img element is set to 200px and the height property is set to 150px.

You can also use percentage values to set the size of the image relative to its parent container. For instance:

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img {
  width: 50%;
  height: auto;
}

In this example, the width property of the img element is set to 50%, meaning the image will take up 50% of its parent container's width. The height property is set to auto, which will maintain the aspect ratio of the image when the width is changed.

Here is a link to the MDN web docs for more information and examples: https://developer.mozilla.org/en-US/docs/Learn/CSS/Styling_images/Set_image_size

To place a div in the center of a page, you can use CSS Flexbox. First, set the parent container's display property to flex and use the justify-content and align-items properties to center the child div. Here's an example code snippet using HTML and CSS:

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<div class="container">
  <div class="centered-div">
    <p>This div is centered!</p>
  </div>
</div>

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.container {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh; /* ensures that the parent container takes up the whole viewport height */
}

.centered-div {
  background-color: #ddd;
  padding: 20px;
}

This will center the centered-div div horizontally and vertically inside the container div. You can adjust the height of the container div to suit your needs. Here's a CodePen example: https://codepen.io/shecodes/pen/xxqXgJp

HTML:

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<div class="container">
  <div class="row">
    <div class="card mx-auto" style="width: 200px; height: 300px;">
        <div class="card-body">
            Card 1
        </div>
    </div>
    <div class="card mx-auto" style="width: 200px; height: 300px;">
        <div class="card-body">
            Card 2
        </div>
    </div>
    <div class="card mx-auto" style="width: 200px; height: 300px;">
        <div class="card-body">
            Card 3
        </div>
    </div>
  </div>
</div>

CSS:

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.card{
  border: solid 1px #ccc;
}

JavaScript:

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// No JavaScript code required for this task 

With CSS you can change the size of your image using the width and height properties. You can specify the size in either percentages or pixels.

For example:

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img {
    width: 70%;
    height: 70%;
} 

This would set the width and height of your image to 70% of the original size.

Alternatively, if you want to set the size in pixels instead, you would use:

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img {
    width: 350px;
    height: 350px;
} 

This would set the width and height of your image to 350 pixels each.

In CSS, you can add a background image behind a container using the background-image property. Here is an example of how you can use this capability:

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.container {
  background-image: url(/background.jpg);
  background-repeat: no-repeat;

  width: 100%;
  height: 500px;

}

To make a container smaller, you can set specific height and width properties to limit the size of the container. For example, in CSS:

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.container {
  width: 500px;
  height: 700px;
}

This will make the container 500px wide and 700px tall. You can also use other length units such as % and vmin, with other properties like min/max-width or min/max-height to adjust the size even further.

You can use the CSS width and height properties to control the size of an image:

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img {
  width: 400px;
  height: 300px;
}