<div class="site-content cf">
  <div class="boxed-group dangerzone">

    <h3>Account</h3>

    <div class="boxed-group-inner">
      <section>
        <h4>Delete this account</h4>

        <button href="#" class="btn btn-danger boxed-action" id="delete-account">Delete Account</button>
        <p>This action is permanent; think twice before proceeding!</p>

        <dialog id="confirm-delete" class="site-dialog">
          <header class="dialog-header">
            <h1>Please Confirm</h1>
          </header>
          <div class="dialog-content">
            <p>You are about to close your account. This action is irreversible. It will permanently delete your account along with its associated data. Are you sure you want to continue?</p>
          </div>
          <div class="btn-group cf">
            <button class="btn btn-danger" id="delete">Delete</button>
            <button class="btn btn-cancel" id="cancel">Cancel</button>

          </div>
        </dialog>

      </section>
    </div>
  </div>
</div>
@gray-darker       : #555;
@gray-dark         : #999;
@gray              : #ddd;
@gray-light        : #f3f3f3;
@gray-lighter      : #e6e9ed;

@body-bg           : #f5f7fa;
@body-color        : @gray-darker;
@header-bg         : #196e76;
@heading-bg        : #434a54;

@button-bg         : @gray-light;
@button-primary-bg : #0074d9;
@button-danger-bg  : #c0392b;

html {
  box-sizing: border-box;
}

*,
*:before,
*:after {
  box-sizing: inherit;
}

.cf:before,
.cf:after {
  display: table;
  content: ' ';
}

.cf:after {
  clear: both;
}

.cf {
  *zoom: 1;
}

body {
  font-family: 'Roboto', Arial, sans-serif;
  margin: 0;
  color: @body-color;
  background-color: @body-bg;
}

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

figure {
  margin: 0;
  padding: 10px;
  a {
    display: block;
  }
}

mark {
  padding: 0 5px;
  background-color: @gray;
}
::backdrop {
  background-color: fadeout(#000, 50%);
}
.btn {
  padding: 10px 15px;

  cursor: pointer;

  color: @gray-darker;
  border-width: 1px;
  border-style: solid;
  border-radius: 3px;
  background-color: @gray-light;
  &.disabled {
    cursor: not-allowed;

    color: @gray;
    border-color: @gray;
  }
}
.btn-group {
  padding: 15px 20px;

  text-align: right;

  background-color: lighten(@gray-lighter, 5%);
}

.btn-primary {
  color: #fff;
  border-color: darken(@button-primary-bg, 5%);
  background-color: @button-primary-bg;
  &:hover {
    background-color: darken(@button-primary-bg, 5%);
  }
}
.btn-danger {
  color: #fff;
  border-color: darken(@button-danger-bg, 5%);
  background-color: @button-danger-bg;
  &:hover {
    background-color: darken(@button-danger-bg, 5%);
  }
}
.btn-cancel {
  color: @gray-dark;
  border-color: @gray;
  &:hover {
    background-color: darken(@button-bg, 5%);
  }
}

.site-header {
  text-align: center;
  background-color: @header-bg;
  h1, a {
    padding: 15px;
    text-transform: uppercase;
    color: #fff;
  }
  h1 {
    font-size: 18px;
    margin: 0;
  }
  a {
    font-size: 14px;
    font-weight: 300;
    display: block;
    text-decoration: none;
    background-color: darken(@header-bg, 10%);
  }
}

.boxed-group {
  width: 90%;
  max-width: 680px;
  margin-top: 50px;
  margin-right: auto;
  margin-left: auto;
  h3, h4 {
    font-weight: 400;
    margin: 0;
  }
  h3 {
    padding: 12px 20px;
    color: #fff;
    border-top-left-radius: 5px;
    border-top-right-radius: 5px;
    background-color: @heading-bg;
  }
  h4 {
    font-size: 18px;
    color: @gray-darker;
  }
  section {
    padding: 30px 20px;
    &:first-child {
      border-bottom: 1px solid @gray-lighter;
    }
    &:only-of-type,
    &:only-child {
      border-bottom: 0;
    }
  }
  .boxed-group-inner {
    font-size: 14px;
    font-weight: 300;
    color: #aaa;
    border-width: 0 1px 1px;
    border-style: solid;
    border-color: @gray-lighter;
    border-bottom-right-radius: 5px;
    border-bottom-left-radius: 5px;
    background-color: #fff;
  }
  .btn {
    float: right;
    margin-left: 20px;
  }
}

.site-dialog {
  overflow: hidden;
  width: 95%;
  max-width: 500px;
  padding: 0;
  border-width: 0;
  border-radius: 5px;
  background: transparent;
  box-shadow: 0 10px 20px 0 rgba(0, 0, 0, .3);
  h1 {
    font-size: 16px;
    font-weight: normal;
    margin: 0;
    color: #fff;
  }
  p {
    font-size: 14px;
  }
  .dialog-header {
    padding: 12px 20px;
    background-color: @heading-bg;
  }
  .dialog-content {
    padding: 30px 20px;
    color: @gray-darker;
    background-color: #fff;
    p:last-of-type, p:only-child {
      margin-top: 0;
      margin-bottom: 0;
    }
  }
}
(function($) {
  'use strict';

  var $accountDelete = $('#delete-account'),
    $accountDeleteDialog = $('#confirm-delete');

  $accountDelete.on('click', function() {
    $accountDeleteDialog[0].showModal();
  });

  $('#cancel').on('click', function() {
    $accountDeleteDialog[0].close();
  });

})(jQuery);

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js