Custom theme for Rocket.Chat

1. Administration > Layout > Color :
   • Content Background Color : #2A2A2A | color
   • Primary Background Color : #242425 | color
   • Primary Font Color : #888889 | color
   • Primary Action Color : #13679A | color
   • Secondary Background Color : #242425 | color
   • Secondary Font Color : #A0A0A0 | color
   • Secondary Action Color : #DDDDDD | color
   • Component Color : #3D3D3E | color
   • Success Color : #095C2C | color
   • Pending Color : #BF360C | color
   • Error Color : #870D0D | color
   • Selection Color : #0D4987 | color
   • theme-color-attention-color : #9C27B0 | color
2. Administration > Layout > Custom CSS :

   * {
       border-radius: 0 !important;
   }
   
   .message .reactions > li.selected {
       border-color: #3D3D3E;
       background-color: #242425;
   }
   
   .message .reactions > li {
       border-color: #000;
       background-color: #242425;
   }
   
   .code-colors {
       background-color: #333334;
       border-color: #333334;
       color: #FFF;
   }
   
   .side-nav .footer {
       background: url(/assets/logo) 50% no-repeat;
       background-size: cover;
   }
   
   .message-form .message-buttons:hover {
       background-color: #1D1D1F;
   }
   
   .page-settings .section {
       border: 1px solid #3D3D3E;
       background-color: #282828;
   }
   
   .page-settings .section-content .input-line {
       border-bottom: 1px solid #3D3D3E;
   }
   
   .message-form .message-form-text.editing {
       background-color: #222;
   }
   
   .background-info-font-color {
       background-color: #0D4987;
   }
   
   .hljs {
       display: block;
       overflow-x: auto !important;
       padding: 0.5em !important;
       background: #2B2B2B !important;
       color: #BABABA !important;
   }
   
   .hljs-strong,
   .hljs-emphasis {
       color: #A8A8A2 !important;
   }
   
   .hljs-bullet,
   .hljs-quote,
   .hljs-link,
   .hljs-number,
   .hljs-regexp,
   .hljs-literal {
       color: #6896BA !important;
   }
   
   .hljs-code,
   .hljs-selector-class {
       color: #A6E22E !important;
   }
   
   .hljs-emphasis {
       font-style: italic !important;
   }
   
   .hljs-keyword,
   .hljs-selector-tag,
   .hljs-section,
   .hljs-attribute,
   .hljs-name,
   .hljs-variable {
       color: #CB7832 !important;
   }
   
   .hljs-params {
       color: #B9B9B9 !important;
   }
   
   .hljs-string {
       color: #6A8759 !important;
   }
   
   .hljs-subst,
   .hljs-type,
   .hljs-built_in,
   .hljs-builtin-name,
   .hljs-symbol,
   .hljs-selector-id,
   .hljs-selector-attr,
   .hljs-selector-pseudo,
   .hljs-template-tag,
   .hljs-template-variable,
   .hljs-addition {
       color: #E0C46C !important;
   }
   
   .hljs-comment,
   .hljs-deletion,
   .hljs-meta {
       color: #7F7F7F !important;
   }
   
   .flex-tab input:focus,
   .flex-tab select:focus,
   .flex-tab textarea:focus {
       border-color: #888889;
   }

3. Enjoy!

MIT