Демонстрация border-radius

https://webref.ru/layout/learn-html-css/box-model

by webref

HTML

<code class="border-rounded">5px</code>

<code class="border-circle">50%</code>

<code class="border-football">15px 75px</code>

CSS

code {
  background: #eaeaed;
  color: #666;
  font: 14px/24px "Source Code Pro", Inconsolata, "Lucida Console", Terminal, "Courier New", Courier;
  display: inline-block;
  height: 90px;
  line-height: 90px;
  margin: 0 14px;
  text-align: center;
  width: 90px;
}
.border-rounded {
  border-radius: 5px;
}
.border-circle {
  border-radius: 50%;
}
.border-football {
  border-radius: 15px 75px;
}