QR-code-component

Replace <div class="q-text"> with the main tag , <span class="b-t"> with <h1> and <span class="s-t"> with <p> to fix the accessibility issues. click here for more on web-accessibility and semantic html

There is no need for <br> in the html.

To center .qr-text on the page using flexbox or grid instead of margin, add min-height:100vh; display: flex; align-items: center: justify-content: center; or min-height:100vh; display: grid place-items: center to the body.

USING FLEXBOX:
body{
min-height: 100vh;
display: flex;
align-items: center;
justify-content: center;
}

USING GRID:
body{
min-height: 100vh;
display: grid;
place-items: center;
}

For responsive content, replace the width in .qr-text with max-width and increase it value, give it a padding value for all the sides max-width: 320px padding: 16px and give the img max-width: 100% and a border-radius value.

Give h1 and p the same font-size of 15px which is 0.9375rem, text-align: center,the same margin-left, margin-right and margin-top values. Give p a margin bottom value.

Use relative units like rem or em as unit for the padding, margin, width values and preferably rem for the font-size values, instead of using px which is an absolute unit. For more on CSS units Click here

Hope am helpful.

Well done for completing this challenge. HAPPY CODING