style.css

.--dark-theme {
  --chat-background: rgba(10, 14, 14, 0.95);
  --chat-panel-background: #131719;
  --chat-bubble-background: #14181a;
  --chat-bubble-active-background: #171a1b;
  --chat-add-button-background: #212324;
  --chat-send-button-background: #8147fc;
  --chat-text-color: #a3a3a3;
  --chat-options-svg: #a3a3a3;
}

body {
  background: url(https://images.unsplash.com/photo-1495808985667-ba4ce2ef31b3?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=1050&q=80);
  background-size: cover;
}

#chat {
  background: var(--chat-background);
  max-width: 600px;
  margin: 25px auto;
  box-sizing: border-box;
  padding: 1em;
  border-radius: 12px;
  position: relative;
  overflow: hidden;
}
#chat::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: url(https://images.unsplash.com/photo-1495808985667-ba4ce2ef31b3?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=1050&q=80) fixed;
  z-index: -1;
}
#chat .btn-icon {
  position: relative;
  cursor: pointer;
}
#chat .btn-icon svg {
  stroke: #FFF;
  fill: #FFF;
  width: 50%;
  height: auto;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}
#chat .chat__conversation-board {
  padding: 1em 0 2em;
  height: calc(100vh - 55px - 2em - 25px * 2 - .5em - 3em);
  overflow: auto;
}
#chat .chat__conversation-board__message-container.reversed {
  flex-direction: row-reverse;
}
#chat .chat__conversation-board__message-container.reversed .chat__conversation-board__message__bubble {
  position: relative;
}
#chat .chat__conversation-board__message-container.reversed .chat__conversation-board__message__bubble span:not(:last-child) {
  margin: 0 0 2em 0;
}
#chat .chat__conversation-board__message-container.reversed .chat__conversation-board__message__person {
  margin: 0 0 0 1.2em;
}
#chat .chat__conversation-board__message-container.reversed .chat__conversation-board__message__options {
  align-self: center;
  position: absolute;
  left: 0;
  display: none;
}
#chat .chat__conversation-board__message-container {
  position: relative;
  display: flex;
  flex-direction: row;
}
#chat .chat__conversation-board__message-container:hover .chat__conversation-board__message__options {
  display: flex;
  align-items: center;
}
#chat .chat__conversation-board__message-container:hover .option-item:not(:last-child) {
  margin: 0 0.5em 0 0;
}
#chat .chat__conversation-board__message-container:not(:last-child) {
  margin: 0 0 2em 0;
}
#chat .chat__conversation-board__message__person {
  text-align: center;
  margin: 0 1.2em 0 0;
}
#chat .chat__conversation-board__message__person__avatar {
  height: 35px;
  width: 35px;
  overflow: hidden;
  border-radius: 50%;
  -webkit-user-select: none;
     -moz-user-select: none;
      -ms-user-select: none;
          user-select: none;
  ms-user-select: none;
  position: relative;
}
#chat .chat__conversation-board__message__person__avatar::before {
  content: "";
  position: absolute;
  height: 100%;
  width: 100%;
}
#chat .chat__conversation-board__message__person__avatar img {
  height: 100%;
  width: auto;
}
#chat .chat__conversation-board__message__person__nickname {
  font-size: 9px;
  color: #484848;
  -webkit-user-select: none;
     -moz-user-select: none;
      -ms-user-select: none;
          user-select: none;
  display: none;
}
#chat .chat__conversation-board__message__context {
  max-width: 55%;
  align-self: flex-end;
}
#chat .chat__conversation-board__message__options {
  align-self: center;
  position: absolute;
  right: 0;
  display: none;
}
#chat .chat__conversation-board__message__options .option-item {
  border: 0;
  background: 0;
  padding: 0;
  margin: 0;
  height: 16px;
  width: 16px;
  outline: none;
}
#chat .chat__conversation-board__message__options .emoji-button svg {
  stroke: var(--chat-options-svg);
  fill: transparent;
  width: 100%;
}
#chat .chat__conversation-board__message__options .more-button svg {
  stroke: var(--chat-options-svg);
  fill: transparent;
  width: 100%;
}
#chat .chat__conversation-board__message__bubble span {
  width: -webkit-fit-content;
  width: -moz-fit-content;
  width: fit-content;
  display: inline-table;
  word-wrap: break-word;
  background: var(--chat-bubble-background);
  font-size: 13px;
  color: var(--chat-text-color);
  padding: 0.5em 0.8em;
  line-height: 1.5;
  border-radius: 6px;
  font-family: "Lato", sans-serif;
}
#chat .chat__conversation-board__message__bubble:not(:last-child) {
  margin: 0 0 0.3em;
}
#chat .chat__conversation-board__message__bubble:active {
  background: var(--chat-bubble-active-background);
}
#chat .chat__conversation-panel {
  background: var(--chat-panel-background);
  border-radius: 12px;
  padding: 0 1em;
  height: 55px;
  margin: 0.5em 0 0;
}
#chat .chat__conversation-panel__container {
  display: flex;
  flex-direction: row;
  align-items: center;
  height: 100%;
}
#chat .chat__conversation-panel__container .panel-item:not(:last-child) {
  margin: 0 1em 0 0;
}
#chat .chat__conversation-panel__button {
  background: grey;
  height: 20px;
  width: 30px;
  border: 0;
  padding: 0;
  outline: none;
  cursor: pointer;
}
#chat .chat__conversation-panel .add-file-button {
  height: 23px;
  min-width: 23px;
  width: 23px;
  background: var(--chat-add-button-background);
  border-radius: 50%;
}
#chat .chat__conversation-panel .add-file-button svg {
  width: 70%;
  stroke: #54575c;
}
#chat .chat__conversation-panel .emoji-button {
  min-width: 23px;
  width: 23px;
  height: 23px;
  background: transparent;
  border-radius: 50%;
}
#chat .chat__conversation-panel .emoji-button svg {
  width: 100%;
  fill: transparent;
  stroke: #54575c;
}
#chat .chat__conversation-panel .send-message-button {
  background: var(--chat-send-button-background);
  height: 30px;
  min-width: 30px;
  border-radius: 50%;
  transition: 0.3s ease;
}
#chat .chat__conversation-panel .send-message-button:active {
  transform: scale(0.97);
}
#chat .chat__conversation-panel .send-message-button svg {
  margin: 1px -1px;
}
#chat .chat__conversation-panel__input {
  width: 100%;
  height: 100%;
  outline: none;
  position: relative;
  color: var(--chat-text-color);
  font-size: 13px;
  background: transparent;
  border: 0;
  font-family: "Lato", sans-serif;
  resize: none;
}

@media only screen and (max-width: 600px) {
  #chat {
    margin: 0;
    border-radius: 0;
  }
  #chat .chat__conversation-board {
    height: calc(100vh - 55px - 2em - .5em - 3em);
  }
  #chat .chat__conversation-board__message__options {
    display: none !important;
  }
}