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CSS

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HTML 

              
                <div class="mail-container">
  <h1>You've got mail</h1>
  
  <div class="content">
    <div class="sidebar">
      <div class="filters">
        <h2>Inboxes</h2>
        <ul class="inboxes">
          <li><div class="icon">📨</div> Primary</li>
          <li><div class="icon">📤</div> Sent</li>
          <li><div class="icon">🗑️</div> Trash</li>
        </ul>
      </div>
      <div class="starred">
        <h2>Favorites</h2>
        <ul>
          <li class="item">
            <div class="context-area">
              <input type="checkbox">
              <div class="star">⭐️</div>
            </div>
             <div class="sender">Jane</div>
             <div class="title">Dinner Invitation: Saturday, May 24</div>
             <div class="time">12:53 PM</div>
          </li>
          <li class="item">
            <div class="context-area">
              <input type="checkbox">
              <div class="star">⭐️</div>
            </div>
             <div class="sender">NYC Events</div>
             <div class="title">[Action Needed] RSVP to Discodome</div>
             <div class="time">9:16 AM</div>
          </li>
          <li class="item">
            <div class="context-area">
              <input type="checkbox">
              <div class="star">⭐️</div>
            </div>
             <div class="sender">Yourself</div>
             <div class="title">Reminder: Pick up Dry Cleaning</div>
             <div class="time">12:23 AM</div>
          </li>
        </ul>
      </div>
    </div>

    <div class="inbox">
      <h2>Primary</h2>
      <ul>
        <li class="item">
          <div class="context-area">
            <input type="checkbox">
            <div class="star">⭐️</div>
          </div>
           <div class="sender">Jane</div>
           <div class="title">Dinner Invitation: Saturday, May 24</div>
           <div class="time">12:53 PM</div>
        </li>
        <li class="item">
          <div class="context-area">
            <input type="checkbox" checked>
          </div>
           <div class="sender">Disco Pants</div>
           <div class="title">Last chance to save on our spring sale</div>
           <div class="time">12:40 AM</div>
        </li>
        <li class="item">
          <div class="context-area">
            <input type="checkbox">
          </div>
           <div class="sender">Flixstr</div>
           <div class="title">Your subscription is about to expire</div>
           <div class="time">12:23 AM</div>
        </li>
        <li class="item">
          <div class="context-area">
            <input type="checkbox">
          </div>
           <div class="sender">Dr. Mew</div>
           <div class="title">Schedule your next appointment with us</div>
           <div class="time">11:23 AM</div>
        </li>
        <li class="item">
          <div class="context-area">
            <input type="checkbox">
          </div>
           <div class="sender">Service.com</div>
           <div class="title">Your feedback is important to us</div>
           <div class="time">11:04 AM</div>
        </li>
        <li class="item">
          <div class="context-area">
            <input type="checkbox">
            <div class="star">⭐️</div>
          </div>
           <div class="sender">NYC Events</div>
           <div class="title">[Action Needed] RSVP to Discodome</div>
           <div class="time">9:16 AM</div>
        </li>
        <li class="item">
          <div class="context-area">
            <input type="checkbox">
          </div>
           <div class="sender">Rachel Smith</div>
           <div class="title">Get ready for your upcoming event!</div>
           <div class="time">5:32 AM</div>
        </li>
        <li class="item">
          <div class="context-area">
            <input type="checkbox">
          </div>
           <div class="sender">Amorzon</div>
           <div class="title">Your order has shipped!</div>
           <div class="time">April 28</div>
        </li>
        <li class="item">
          <div class="context-area">
            <input type="checkbox">
          </div>
           <div class="sender">The Foundation Foundation</div>
           <div class="title">Join our team of volunteers today</div>
           <div class="time">April 28</div>
        </li>
        <li class="item">
          <div class="context-area">
            <input type="checkbox">
          </div>
           <div class="sender">Daily Traveler</div>
           <div class="title">Travel inspiration for your next vacation</div>
           <div class="time">April 28</div>
        </li>
      </ul>
    </div>
    <div class="bottom-bar">
      <div class="pagination">➡️</div>
    </div>
  </div>
</div>
!

CSS 

              
                /* :has() stuff */

.item:has(.star) {
  background: #eee;
}

.item:has(:checked) {
  background: Highlight;
}

.item:has(.star) .title,
.item:has(.star) .time {
  font-weight: 800;
}

/* Inbox */

.item {
  display: grid;
  grid-template-columns: 5rem 1fr 4fr 1fr;
  gap: 1rem;
  border: 1px solid lightgray;
  padding: 0.5rem;
  align-items: center;
  justify-items: start;
}

.item + .item {
  border-top: none;
}

.bottom-bar {
  display: flex;
  justify-content: flex-end;
  background: #eee;
  padding: 1rem;
  border-bottom: 1px solid lightgray;
  border-right: 1px solid lightgray;
  border-left: 1px solid lightgray;
  display: none;
}

.title,
.sender {
  width: 100%;
  overflow: hidden;
  white-space: nowrap;
  text-overflow: ellipsis;
}

.mail-container {
  max-width: 1200px;
  margin: 0 auto;
}

.content {
  display: grid;
  grid-template-columns: 300px 3fr;
  gap: 2rem;
}

.context-area {
  display: flex;
  gap: 0.25rem;
  align-items: center;
}

[type="checkbox"] {
  width: 1.25rem;
  height: 1.25rem;
}

/* Base */

body {
  font-family: 'Google Sans', system-ui;
  padding: 1rem;
}

h1 {
  font-size: 3rem;
  margin: 1rem 0 2rem;
}


h2 {
  font-size: 1.5rem;
  font-weight: 300;
  margin-bottom: 1rem;
}
.inboxes li {
  background: aliceblue;
  border: 1px solid powderblue;
  border-radius: 20px;
  padding: 0.5rem 1rem;
  margin-bottom: 0.25rem;
  display: grid;
  grid-template-columns: 1.5rem 1fr;
  gap: 1rem;
}

.starred {
  margin-top: 2rem;
}

/* MQ */
@media (width <= 850px) {
  .content {
    grid-template-columns: 1fr;
  }
  
  .sidebar {
    display: grid;
    grid-template-columns: 200px 1fr;
    gap: 1rem;
  }
  
  .starred {
    margin-top: 0;
  }
}

@media (width <= 550px) {
   .sidebar {
    grid-template-columns: 1fr;
  }
}

/* CQ Bits */

.inbox {
  container: inbox / inline-size;
}

.starred {
  container: starred / inline-size;
}

@container (width <= 550px) {
  .item {
    grid-template-columns: 3.5rem 1fr 4fr;
  }
  
  .time {
    display: none;
  }
}
!

JS
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