<div class="container">
  <div class="top" contenteditable="true" spellcheck="false">
    Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. 
  </div>
  <div class="bottom" contenteditable="true" spellcheck="false">
    Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. 
  </div>
</div>

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
<div class="container">
  <div class="top">
    Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
  </div>
  <div class="bottom">
    Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
  </div>
</div>

:root {
  --padding: 5px;
  --border-width: 3px;
  --border-color: #fff;
  --border-radius: 15px;

  --right-space-width: 100px;
  --right-space-height: 50px;
  
  --border: var(--border-width) solid var(--border-color);
}

.top,
.bottom {
  position: relative;
  box-sizing: border-box;
}

.bottom::before,
.bottom::after,
.top::before,
.top::after,
.container::before,
.container::after {
  display: block;
  position: absolute;
  box-sizing: border-box;
}

.top,
.top::before,
.bottom,
.bottom::after,
.bottom::before,
.container::before {
  background-image: inherit; 
  background-attachment: fixed;
}

.top::before,
.top::after,
.container::before,
.container::after,
.bottom::before,
.bottom::after {
  content: "";
}

.container {
  background-image: linear-gradient(120deg, #fff, #fa5);
  background-size: 0;
  background-repeat: no-repeat;
  filter: drop-shadow(0 0 0.75rem #000);
}

.container::before {
  /* Вогнутый уголок справа */
  
  width: var(--border-radius);
  height: var(--border-radius);

  right: calc(var(--right-space-width) - var(--border-radius));
  bottom: calc(var(--right-space-height) - var(--border-radius) );

  /* clip-path: path('M 0 0 L 0 15 Q 2 2 15 0'); */
  mask: radial-gradient(
    circle at 100% 100%, 
    #0000, 
    #0000 calc(var(--border-radius) - var(--border-width) + 1px), 
    #000 calc(var(--border-radius) - var(--border-width) + 1px), 
    #000
  );
}

.container::after {
  /* Граница вогнутого уголка справа */
  
  width: var(--border-radius);
  height: var(--border-radius);

  right: calc(var(--right-space-width) - var(--border-radius) );
  bottom: calc(var(--right-space-height) - var(--border-radius));

  border: var(--border);
  border-right: none;
  border-bottom: none;

  border-radius: var(--border-radius) 0 0 0;
}

.top {
  margin-left: 50%;
  
  min-height: calc(var(--border-radius) * 2 );

  padding: var(--padding);
  border: var(--border);
  border-bottom: none;
  border-radius: var(--border-radius) var(--border-radius) 0 0; 
}

.top::before {
  /* Вогнутый уголок слева */
  width: var(--border-radius);
  height: var(--border-radius);

  left: calc(0px - var(--border-radius));
  bottom: 0;

  /*clip-path: path('M 15 15 L 0 15 Q 13 13 15 0');*/
  mask: radial-gradient(
    circle at 0 0, 
    #0000, 
    #0000 calc(var(--border-radius) - var(--border-width) + 1px), 
    #000 calc(var(--border-radius) - var(--border-width) + 1px), 
    #000
  );
}

.top::after {
  /* Граница вогнутого уголка слева */
  width: var(--border-radius);
  height: var(--border-radius);

  left: calc(0px - var(--border-radius));
  bottom: 0;

  border: var(--border);
  border-left: none;
  border-top: none;
  border-radius: 0 0 var(--border-radius) 0;
}

.bottom {
  background-size: 0;
  
  min-height: calc(var(--right-space-height) + var(--border-radius) + var(--border-width));
  
  padding: calc(var(--border-width) + var(--padding));
  padding-right: calc(var(--right-space-width) + var(--padding));
  padding-top: var(--padding);
}

.bottom::before {
  /* Подложка нижней части слева */
  
  top: calc(0px - var(--border-width));
  bottom: 0;
  left: 0;
  right: calc(var(--right-space-width) - var(--border-width));
  z-index: -1;
  
  border: var(--border);
  border-radius: var(--border-radius) 0 var(--border-radius) var(--border-radius);
}

.bottom::after {
  /* Подложка нижней части справа */
  z-index: -1;
  
  width: var(--right-space-width);
  top: calc(0px - var(--border-width));
  right: 0;
  bottom: calc(var(--right-space-height) - var(--border-width));

  border: var(--border);
  border-left: none;
  border-radius: 0 0 var(--border-radius) 0;
}


/* для демо */
:read-write {
  cursor: pointer;
}
:read-write:focus {
  outline: none;
}